_DO SNAKES INCUBATE THEIR EGGS?_
WE come now to treat of facts no less interesting than surprising in
ophidian biographies. Already we have recounted almost marvellous
powers possessed by this class of animals—functions which are
volitionary, such as the management of their trachea, the voluntary
folding back or unfolding of certain teeth, the practical adaptation of
their ribs and coils to what we may almost call manual work, and now,
most astonishing of all, the voluntary deposition or retention of ova,
even of young.
‘Snakes are either oviparous or viviparous,’ is what we are accustomed
to read, followed by the explanation that the former are those which
lay eggs, and the latter those which produce their young alive. To
these two chief distinctions, the more recent one of ovoviviparous
has been added, to describe some intermediate cases where the egg is
ruptured in parturition, so that again a fully-formed young one is
born. For broad distinctions the three terms do well enough, though
many exceptions exist. The grand distinction of ‘_viper_’ as applied
to those snakes which produce live young, was adopted when snakes were
first observed and described by classic writers.
‘Vipers alone are viviparous,’ wrote Aristotle. ‘Sometimes the little
vipers eat through their mother and come forth. The viper brings forth
one at a time in one day, but she brings forth more than twenty little
vipers. Other serpents produce their eggs externally, and these eggs
are connected with each other like the necklaces of women. But when
they bring forth, they deposit their eggs in the earth, _and there
incubate them_. These eggs they disclose the following year.’ We do not
quote the above as all fact, but rather to show how very much there has
been to _unlearn_ since Aristotle was accepted as an authority. The
shadow of truth and the mention of a possible fact as an invariable
rule are dangerous mistakes, for, as we have already shown, where a
snake is concerned, one can rarely feel safe in asserting anything as
positive. It is not impossible that, owing to disease or accident,
some gravid viper may have been so wounded as to enable her young to
make their début through her ruptured side. Such an occurrence has
been seen in our own time. Aristotle or his authority may even have
witnessed such an accident, and recorded it under the supposition that
it was normal. In whatever way the error may have originated, it is
only one out of many that are propagated even to the present day by the
uninformed.
At the moment of writing, we read in one of our first-class ‘dailies,’
alluding to a brood of young vipers lately born at the Zoological
Gardens: ‘The young viper comes into the world in the shape of an
egg, and its first business is to push through the filmy membrane
which envelops it in its imprisoned form.’ This is contrary to our
accepted ideas, though partially true in this instance. The word
viper is generally supposed to be derived from the Latin _vipera_, a
contraction of _vivipara_, to produce alive. The above words therefore
are inapplicable as a rule.
So far as was known in Aristotle’s time, only certain venomous species
common in the countries with which classic writers were best acquainted
did produce live young, and they were mostly what are still known as
‘vipers,’ a term restricted to these and explained as being derived
from such signification.
Opportunities of study and of observation afforded in menageries and
zoological gardens at the present day have caused the term _viper_ as
relating to gestation to be discarded, or many non-venomous snakes must
be included, thus overthrowing all our notions of vipers. As was shown
in the preceding chapters, the name is now associated with dentition.
German and French ophiologists affirm that the three distinctions of
_oviparous_, _viviparous_, and _ovoviviparous_ are founded on no other
ground than the greater or less development of the fœtus at the time of
deposition.
The nature of the egg-covering or ‘shell’ has also to do with this. In
eggs which take a longer time to mature or to ‘hatch,’ the external
covering is thicker and more leathery; in those which are hatched
either before or on deposition, the shell is thinner, more membranous.
Always, however, there is a calcareous element in the shell, and the
eggs are generally, _but not invariably_, linked together.
Heat and moisture are essential to the hatching of eggs. When at
liberty the snake selects some spot among decaying leaves, or in a
manure heap where decomposition produces sufficient warmth. In the
tropics, where the sun’s rays alone suffice, a soft moist bed is more
easily found, and here it is that immense broods are produced.
The period of gestation can scarcely be pronounced upon with certainty.
It depends not only on the size of the snake, but on the degree of
warmth that can be enjoyed as an assistant to mature the eggs. Schlegel
mentions three or four months from copulation to the laying of eggs in
the species indigenous to France. But as other circumstances combine to
cause variations in these periods, it is very unsafe to fix upon the
precise time of gestation.
Says Rymer Jones, ‘Reptiles do not sit (_sic_) upon their eggs, hence
the latter have only a membranous envelope. In many of the reptiles
which lay eggs, especially the _Colubri_ (colubrine snakes), the
young one is already formed and considerably advanced in the egg at
the moment when the mother lays it; and it is the same with those
species which may at pleasure be rendered viviparous by retarding their
laying.’[129] The latter words are traced to Cuvier, and prove that
this most remarkable power has long been recognised.
In the first few words of the above, Jones spoke of reptiles generally
from toads to turtles; with the latter, soft eggs would certainly fare
badly did they attempt to incubate them. Still the term ‘reptiles’ is
misleading, because, as is now well known, some snakes do incubate,
and some lizards are suspected of doing the same. Even our common ring
snake has been found coiled upon her eggs.
Serpents are allied to birds in producing young from eggs, but in
reptiles the eggs differ from those of birds in undergoing a sort of
incubation from the very first; so that at whatever period a snake’s
egg is examined, whether it has been laid or not, the embryo will
be found more or less advanced. Sometimes in an egg just deposited,
a perfectly formed fœtus will be found. ‘Serpents are _always_
oviparous,’ says Schlegel; ‘and it is a mistake to suppose that all
venomous snakes produce live young, and all non-venomous kinds lay
eggs. Neither has the diversity of generation any relation to the
organization of the animal itself. _Coronella lævis_ produces living
young, but other _coronellas_ lay eggs. In 1862, when very little was
known of the _Coronella lævis_, Mr. Frank Buckland had one in a cage in
London, which to the surprise of most persons produced live young ones.
This may have been solely owing to her captivity and her retention
of eggs till hatched. Some boas lay eggs, others are viviparous. In
the latter case the young are enclosed in a thin membrane, which they
tear or break at the moment of birth. In those that are a long while
hatching, the tunic is of a thick, coriaceous texture, not easily
ruptured. Thus, to sum up with one other authority, Der Hœven: ‘In many
serpents and lizards the development begins in the body of the parent
before the egg is laid, and in some the membrane of the egg is broken
by the young one before birth.’
This latter condition has been considered viperine, but even in a
viper the young have been produced in a membrane. This was the case
with _Vipera nasicornis_ at the London Zoological Gardens, on Sunday,
November 6th, 1881, that gave birth to forty-six viperlings. Some of
them had no vestige of membrane clinging about them; others had, but
burst it immediately and began to crawl; while yet others did not burst
their ‘shell’ at all,—if indeed so filmy and thin a membrane could
be called a shell,—but died within it. When the membrane burst, it
was seen to collapse and shrivel up into nothing, as children’s air
balls do when they are torn; but the texture of these balls is strong
in comparison with the extreme tenuity of the viperine egg tunic. Yet
it was strong enough to contain a young one, as in the case of those
unbroken. There is no means of ascertaining the precise length of time
this viper had been in captivity; but as her young ones had all such
fully-developed fangs, and the precocity to strike and kill a mouse as
soon as born, this was probably another case of postponed deposition.
On a previous occasion, September 1875, a family of young vipers born
at the Ophidarium were ‘_some quite clean and others with the remains
of the egg covering about them_.’ The quotation from my notebook refers
to the Daboia of India, ‘Russell’s viper’ (_Vipera elegans_). Still
these may be exceptional and possibly abnormal cases, but are examples
worth noting, and another proof of the many exceptions to what we are
accustomed to believe invariable rules.
White, in his _History of Selborne_, mentions the capture of a viper
in which he found fifteen young, the shortest being seven inches. They
were active, spiteful, and menacing, and yet ‘had no manner of fangs
that we could find, even with the help of our glasses.’
Mr. Frank Buckland tells of a man who cut open a string of snake’s
eggs, and the young, thus prematurely introduced into the world,
‘showed fight.’
Of historical ophidians which have figured in many pages, first comes
chronologically the Paris python, that in 1841 laid fifteen eggs and
incubated them. She has already been alluded to in chap. iv., but
claims further mention presently.
A python in the Amsterdam collection next hatched twenty-two eggs.
In 1862 a python at the London Gardens laid above a hundred
eggs,—‘more than a bushel,’ according to the keeper,—and settled
herself to hatch them. Much interest attaches itself to this lady’s
history; but first to complete our list chronologically, the following
harmless species in the London collection have within the last ten
years produced live young, being examples of that ‘diversity of
generation’ of which Schlegel speaks.
August 1872, the ‘seven-banded snake’ (_Trop. leberis_) had five young
and some eggs at the same time.
June 1873, a _Coluber natrix_ had seven young ones. (I cannot affirm
positively that these were born alive; I think not, from an especial
entry in my notebook concerning them; but the records of the Zoological
Society in which I have sought for confirmation do not announce them as
‘hatched.’)
August 1873, a yellow Jamaica boa (_Chilobothrus inornatus_) gave birth
to fourteen young ones, ten of which survived. They crawled up to the
top of their cage as soon as they saw daylight, and showed signs of
fight. One little aggressor struck at me when I held it, and tried
to bite me through my glove,—an impertinence which was permitted in
order to test its powers. It constricted my fingers as tightly as if
a strong cord were wound round them, and when not thus occupied it
wriggled and twisted itself about in such energetic contortions that
I could scarcely hold it. The activity and daring of the whole fry
proved their perfect development. On another occasion the same species
produced eight, and on a third occasion thirty-three young ones, but of
these dates I am not quite sure. In some cases a few eggs were produced
at the same time, but they were hard and bad and of the consistency
of soap. The manners and actions of the three equally well-developed
families were similar. They were always on the defensive, and able to
fight their own battles. When the keeper put his hand into the cage,
they seized upon it and held on with their teeth so tightly that on
raising it they hung wriggling and undulating like a living, waving
tassel.
Another boa from Panama, on 30th June 1877, had twenty young, which
displayed ability to take care of themselves forthwith by leaving
the marks of their teeth on Holland’s fingers. These twenty were all
produced during the night, or before the arrival of the keeper the next
morning, and were lively and spiteful, biting any one who attempted
to touch them, and sharply enough to draw blood. Mr. E. W. Searle,
who described them in _Land and Water_ at the time, July 1877, said:
‘This is probably the first recorded instance of the breeding of boa
constrictors in captivity.’ He seemed also to infer that this proved
the boa to be viviparous instead of oviparous, as ‘had been always
understood.’ Having already known of cases of abnormal, and also of
postponed production of eggs or of young, I ventured at the time to
cite such cases in _Land and Water_, July 7, 1877, adding: ‘We must not
too hastily conclude that because one boa constrictor produced a family
of lively young ones, this species is invariably viviparous.’ Also in
the _Field_, July 14, 1877, I suggested that ‘the circumstance might be
received rather as a further example of snakes breeding under abnormal
conditions,’—opinions further confirmed by subsequent observations.
The little fry were supplied with young mice, which they constricted
as if they had served an apprenticeship; but the mother left them
entirely to themselves, and betrayed no other unusual feelings than to
hiss when disturbed. When they were seven weeks old, they in one night
ate twenty-four mice and a few young rats between them. They all cast
their first coat before they were a week old. The mother had been in
the Gardens about eight years. All but one of this fine family were
alive in the following November, and two are still living at the time
of going to press, viz. ‘Totsey’ (illus. p. 201) and one brother.
The dates of these few following cases are a little uncertain, also
exactly how many survived of those that were born.
A ‘seven-banded’ snake (_Trop. leberis_) had six.
A ‘chicken snake’ (_Col. eximius_).
A ‘moccasin snake’ (_Tropidonotus fasciatus_) had nine young ones.
This species has sometimes produced young and eggs at the same time.
A ‘garter snake’ (_Tropidonotus ordinatus_).
A boa constrictor had eight pretty little active snakelings that at
two days old pretended to constrict my fingers, and forcibly enough to
prove their powers.
On two occasions at the Gardens within the time specified, hybrids have
been born between _Epicratis angulifer_ and _Chilobothrus inornatus_,
and I can but think that occurrences of this nature must happen among
snakes in their wild state occasionally, which may throw some light on
the perplexities of classifiers.
In August 1878, three were born alive; and in recording the event the
Secretary to the Zoological Society, P. Lutley Sclater, Esq., Ph.D.,
F.R.S., etc., writes that there can be no question as to the pairing
of these two snakes, both in the same cage, and as there was no male
_Epicratis_ in the collection. Three were alive and six bad eggs were
produced.
In September 1879, two more hybrids were born between the same pair;
who, at any rate, remained constant to each other.
Of the venomous serpents that have fallen under my own notice at
the Zoological Gardens, the little Indian viper (_Echis carinata_)
had three young ones in July 1875. Only two survived a few weeks.
They changed their coat at an early day, but ate nothing; nor did
the mother, who soon died. One may mention here that the vipers in
collections rarely do survive long after giving birth to young. This
may be only owing to an unhealthy condition in captivity, but merits
inquiry.
Four common adders (_Vipera berus_) and several broods of the Daboia
have also been produced.
The African viper of the coloured illustration is another example, as
having afforded opportunities for observation.
In point of numbers we find the families varying from three or four
to upwards of a hundred. When the parent is in health, the young
are produced easily and rapidly. _Vipera nasicornis_ deposited her
forty-six children within about three hours. A Java snake (though
not in our London Ophidarium) produced twenty-four young ones in
twenty minutes. Anaconda, in April 1877, on the contrary, exhibited
considerable protraction, extruding bad eggs at irregular intervals for
many days. She will form the subject of the next chapter.
Incubation, or the hatching of eggs by the maternal warmth, seems not
to have been suspected by ophiologists until a comparatively recent
date; but by the non-scientific, the barbarian and the untutored
natives of hot countries, who see, but dream not that in future ages
what they saw and incidentally spoke of would be of weight to the
enlightened of as yet unexisting nations,—by such the fact was known
long ere its worth _as a fact_ was recognised. Yet, as has been already
seen in these pages, evidence given without intent and purpose often
is of scientific importance. Aristotle spoke of incubation; but with
classic writers the difficulty of sifting fact from fable may cause the
whole to be rejected.
We owe to Zoological Societies and menageries the confirmation of
the _couvaison_ of at least one species of serpents. Subsequently we
are told, ‘The python only incubates,’ this snake being generally
mentioned as the one exception; and only within a very few years has
maternal affection been accredited to any others. Mr. P. H. Gosse was
informed by the negroes in Jamaica of the habits of the yellow boa. Sir
Joseph Fayrer was informed by the jugglers that ‘over and over again
they had dug cobras out of their holes _sitting on their eggs_.’ Dr. E.
Nicholson was informed ‘on trustworthy authority that the Hamadryad has
been found coiled upon a nest of evidently artificial construction.’ He
thinks snakes always watch over their eggs, and frequent the locality
where they have deposited them. The keeper at the Gardens confirms
this by his own observations. ‘They do care for their eggs in their
own way,’ he assured me, and display unusual irritability and wildness
at such times.[130] In menageries, however, their habits are always
more or less artificial; they cannot seek spots for themselves, or
exercise maternal instinct beyond doing the best they can under the
circumstances. Anything in the way of extra indulgences, such as soft
rubbish, moss, or sand, is duly appreciated when eggs are about to be
deposited, and we find maternal ophidians resort at once to this.
In a footnote, vol. xvi. p. 65 of the _Annales des sciences
naturelles_, we read:—‘_Il parait que l’incubation des serpents
est un fait si connu dans l’Inde, qu’il entre même dans leur contes
populaires. M. Roulin m’a fait remarquer dans le second voyage de
Sindbad le marin_ (_nouvelle traduction Anglaise des ‘Mille et une
nuits’ par W. Lane_, tom. iii. p. 20) _le passage suivant: Alors je
regardai dans la caverne, et vis, au fond, un enorme serpent endormi
sur ses œufs_.’
Here again, by accident, an ophidian habit known in the 8th century has
been revealed to the scientific of the 19th century.
In the 17th century, when the Royal Society was founded and scientific
information of all descriptions was welcome in their published
_Transactions_, the subject of serpent brooding appeared in those
pages. In vol. i. p. 138, a few terse words exactly express what modern
ophiologists have of late years verified. ‘Several have taken notice
that there is a difference between the brooding of Snakes and Vipers;
those laying their Eggs in Dung-hills by whose warmth they are hatched,
but these (Vipers) brooding their Eggs within their Bellies, and
bringing forth live Vipers. To which may be added,—That some affirm to
have seen Snakes lye upon their Eggs as Hens sit upon theirs.’ This was
published in 1665.
The truth of ophidian incubation in at least one species was finally
established at the _Musée d’Histoire_ at Paris in 1841, when _Python
bivittatus_ or _Python à deux-raies_—named from two black lines
diverging from the mouth—incubated her fifteen eggs. This celebrated
serpent has enriched zoological annals in several points of interest.
She assisted to confirm the question of whether snakes drink, and, as
will be seen, whether they will take dead food. In connection with
the present subject, the observations made by M. Dumeril during her
incubation in the months of May and June 1841 are of such interest
that I will translate from a paper read at the _Academy of Sciences_
in Paris, by M. Valenciennes, 19th July 1841, and published in the
_Annales des sciences naturelles_, tom. xvi. 2^{me} série, p. 65. It
will be remembered that M. Dumeril (to whom we are indebted for the
most complete work on _Erpétologie générale_ that graces the shelves of
our Great National Library) was at that time Professeur d’Erpétologie
au Musée de Paris, and specially charged with the management of that
part of the menagerie.
M. Valenciennes began his paper by reminding his audience that the
temperature of birds rises in various degrees during the period of
incubation, proposing the questions, ‘Do reptiles not offer a similar
phenomenon?’ ‘Do they never brood on their eggs?’ As far as was known
of native reptiles, the answer would be in the negative. However, M.
Lamarrepiquot, in his travels in Chandernagor and the isle of Bourbon,
seems to show that a large serpent of India, and some other species,
_se plaçait sur ses œufs et les echauffait en developpant pendant ce
temps une chaleur notable_. Many eminent naturalists doubted this,
until it was confirmed in the Paris python, in which was an example of
prolonged and uninterrupted incubation for the space of fifty-six days.
M. Valenciennes proceeded to describe that she was in a cage with
others, and that a temperature higher than the outside air was
maintained. During January and February she coupled several times,
and in February ate six or seven pounds of raw beef that was tied on
to a live rabbit of middling size. Food offered her afterwards, for
three weeks in succession, she refused; but, as described in chap.
iv., she drank no less than five times during her brooding. Sloughing
occurred on the 4th April. Generally gentle and quiet, she became
excited on the 5th May, and tried to bite any one who approached her.
Her condition being evident, she had been left alone and undisturbed
in her cage; and at six o’clock on the morning of the 6th of May, laid
an egg, fourteen others being deposited by half-past nine A.M. The
eggs were soft at first, of an oval form, and an ashy-grey colour,
but afterwards became rounder and of a clear white. They were all
separate. She collected them in a cone-shaped pile, and rolled herself
round them, so as to completely hide every one, her head being at the
summit of the cone. For fifty-six days she kept perfectly motionless,
excepting when manifesting impatience if any one attempted to touch
her eggs. Notwithstanding this want of trustfulness on the part of the
interesting invalid, M. Dumeril achieved some important experiments
regarding her temperature.
Reptiles are ‘obedient to the surrounding temperature,’ we may repeat,
but in the present instance there was warmth in her perceptible to
the touch (_une chaleur notable_). The temperature of the cage was
20° (Reaumur?), that under the woollen coverlet where she reposed
was 21°; but in her coils, where M. Dumeril inserted one of the best
thermometers that could be procured, she was 41°, and always of a
higher temperature by some 20°. Placing the thermometer either upon
her or between the folds of her body, only a slight variation was
perceptible, but it was invariably higher than the surrounding air.
On the 2nd of July one of the shells split (_la coque s’est
fendillée_), and the head of a little python appeared. During that
day the little creature only twisted about within its shell, now its
head, now its tail being visible outside, and withdrawn again. The next
day the wee snake made its debut altogether, and began to crawl about
(_s’est mise à ramper_). It lost no time in exploring to the remotest
corners of its blanket, and by degrees showed itself to the world.
During the next four days eight were similarly hatched, the seven
remaining eggs, at various stages of development, having apparently
been crushed by superincumbent weight.
The mother, on the 3rd of July, ate six more pounds of beef, after her
fast of nearly five months; but with the posterior part of her body
still folded over the eggs. She then quitted them, and displayed no
further care, having covered them for so long a time, and even defended
them with such assiduity. From ten to fourteen days after being
hatched, the young ones all changed their coats, and then ate some
little sparrows, throwing themselves upon them, and constricting them
like grown-up pythons.
M. Valenciennes drew attention to the circumstance that only in hot
countries do serpents incubate their eggs, _i.e._ only the serpents
indigenous to hot countries. In temperate ones, where the average
warmth is insufficient, they resort to artificial heat; as, for
instance, manure heaps, or decaying vegetation.
Thus was this important question settled, and the hatching of the young
brood in Paris became a chronological era in ophidian annals.
When therefore, in January 1862, twenty-one years afterwards, a python
_seba_ in our own Gardens laid upwards of a hundred eggs, immense
interest and curiosity were excited among the zoologists of the day,
for here at home in London was a grand opportunity for observing the
one only snake which at that time was supposed to exhibit any sort of
maternal instinct. Plenty of damp moss had been supplied to her, the
temperature maintained in the cage being supposed sufficient for her
well-being. She pushed the moss into a kind of nest, and when the ‘long
string of eggs’ were deposited, she arranged them in a nearly level
mass, and then coiled herself over and around them so as to hide and
cover them as much as possible. Sometimes she changed her position a
little, and re-arranged her eggs, and in various ways rendered herself
worthy of record.
Ophiologists had scientific facts to verify: this opportunity must
not be neglected for ascertaining whether so cold a nature, and in
midwinter, could produce sufficient warmth by lying there day after
day upon her bushel of eggs. So thermometers were ever and anon thrust
between her coils, or held close to her; first here, then there, after
the example of M. Dumeril in Paris. Other disturbances in the way of
cleaning out the cage and supplying her companion in captivity with
food and water were angrily resented by the poor patient, who had no
chance of the tranquillity that she would have sought for herself in
her native tropics. Besides which, the chances against hatching were
far greater in her case than in the Paris and Amsterdam pythons. The
former saved only eight out of her fifteen, and here we had, in round
numbers, one hundred, more than she could successfully cover at one
time. Moreover, a most untoward accident happened one night by the tank
overflowing among her eggs, necessitating a complete disturbance of
them. What wonder, then, that she was irritable and even savage during
the whole time of her incubation! One egg, examined fifteen days after
it was laid, contained a living embryo, so there were hopes of some
at least maturing. For more than seven weeks she remained patiently
brooding, when all hope of hatching any of the eggs had vanished, and
it became necessary to take them from her. This was done by degrees,
and the task was no easy one. The keeper watched his opportunity to
raise the sliding door at the back of the cage, make a snatch at those
nearest him, and shut down the slide with celerity, or the exasperated
mother would have seized him. He nearly got his arm broken more than
once by the despatch he was compelled to use. Sometimes, so quick was
she, that in thrusting down the slide she was nearly jammed by it.
Holland protected himself by holding up a corner of the rug so as to
hide himself when he had occasion to open the slide door; yet one day
she ‘jumped’ at him, seizing the rug, and with a toss of her head
jerking it back with such violence that a shower of the gravel came
hailing upon the glass in front of the cage, to the consternation and
alarm of the spectators gathered there, and who at the moment imagined
the glass was broken, and that the infuriated reptile would be among
them. But they were behind her; it was only towards the keeper that her
fury was directed: he had taken away the last of her eggs. When, then,
he shut down the slide, she kept her angry eyes fixed upon it for a
long while. Presently she sought in her empty nest, upon which, so long
as any eggs had remained to her, she had re-settled herself after each
irruption. At last she took to her bath, in which she remained for a
long while.
After the scenes witnessed during those seven weeks, no one could doubt
the existence of maternal affection; and this was worth proving, as
some authors would have persuaded us that snakes, and particularly the
non-venomous ones, manifest total indifference regarding their eggs.
The other important fact, an increased temperature, was also again
observable, proving that a serpent can really hatch her eggs by the
warmth of her own body.
Last summer, 1881, another python laid about twenty eggs at the London
Ophidarium, but, alas! neither were any of that brood hatched. For
future broods, now that the fact of a raised temperature has been
proved, the next scientific triumph will be to develop the young ones,
dispensing with thermometers, and substituting perfect tranquillity,
with every possible aid and comfort to the mother.
That snakes under these peculiar circumstances do appreciate little
‘delicate attentions,’ ample proof has been afforded in the Jamaica
‘yellow boa’ (_Chilobothrus inornatus_), the species which on several
occasions has produced broods in London, and the one in which Mr. P.
H. Gosse verified the marvellous instinct of withholding its eggs when
circumstances were not propitious for their deposition. This is one of
the ‘Colubri’ alluded to by T. Rymer Jones, ‘which may at pleasure be
rendered’ (_i.e._ render themselves) ‘viviparous by retarding their
laying.’
But when Gosse published his work on Jamaica (1851), he did not appear
to be aware of what Jones and Cuvier had said on this subject, but
stated the result of his own observations. He had become convinced that
this species of snake forms a sort of nest, and incubates its eggs;
when subsequently, one that he had in captivity produced living young,
he was staggered. ‘Is it possible,’ he wrote, ‘that a serpent normally
oviparous, might retain the eggs within the oviduct until the birth of
her young, when circumstances were not propitious?’
‘Is it possible,’ again asks an American naturalist, so lately as
1879,—‘can it be true that _Heterodon platyrhinos_ and _Tropidonotus
sipedon_’ (both harmless) ‘are sometimes viviparous and sometimes
ovoviviparous?’ This writer, F. W. Cragin, had been told that the two
above species were ovoviviparous (a word of no value as a definition),
and he writes in the _American Naturalist_, vol. xiii. p. 710, that out
of twenty-two eggs of Heterodon, ploughed up out of the sand in Long
Island, one he put into alcohol to preserve it as found, and the others
were hatched on the fourth day, showing that sometimes at least it is
oviparous, as supposed are some of the _Eutænias_.
Mr. Gosse describes one Jamaica boa in confinement, that was ill
and inactive, refusing food. It was unusually vicious, and bit hard
enough to draw blood, the effect of the fine teeth being like a severe
cat-scratch. It rendered itself further offensive when disturbed, by
emitting an insufferable odour, and at length gave birth to living
young.
That this snake when at liberty lays eggs, he had seen, and in a nest
of artificial construction. One that he knew of was excavated in a
bank. The snake was seen issuing from a narrow passage just large
enough to admit it. Dry, crumbled earth had been discharged at the
entrance of the passage, where it lay in a heap. The bank being dug
into, the passage was found to lead to a cavity lined with soft
rubbish, leaves, etc., which must have been carried there. Mr. Gosse
does not pretend to affirm positively that the snake constructed that
secluded nest for itself. It might have done so, pushing out the mould
by the lateral undulations of its body, as the burrowing snakes do,
and carrying back the soft trash in its mouth or, if it only chose a
nest formed by some other animal, this proved maternal care. There
were eggs in the nest, the shell being like ‘white kid.’ ‘On snipping
one, a clear glaire exuded, in which was a large, whitish vitellus,
stained with blood vessels, and containing a young snake seven inches
long, but immature.’ One fœtus writhed. The fœtus being formed and
capable of motion, proved, Mr. Gosse thought, that the eggs had been
some time laid. Incubation is a characteristic of that family, the
author affirms. Of the various cases he knew, one female boa brought
forth eleven snakes. In another snake that was killed, ten or twelve
fully-formed young ones were found.
One of these ‘yellow boas’ in a private collection displayed unusual
restlessness and uneasiness, crawling about its cage as if in search
of something. Those who had the care of it suspected that she was with
eggs, and supplied her with fine sand. This appeased her somewhat, and
after twirling herself around to form it into a kind of nest, she laid
some eggs. One of the same kind at the Gardens accepted gratefully some
soft cotton wool which a lady brought for her and her young progeny,
all of whom nestled themselves in it contentedly and speedily.
Two other noteworthy cases have to be recorded, but they shall form the
subject of the ensuing chapters.
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