By DR. C. V. RILEY.
There is always a great deal of interest attaching to organisms which are
unique in character and which systematists find difficulty in placing in
any of their schemes of classification. A number of instances will occur
to every working naturalist, and I need only refer to Limulus, and the
extensive literature devoted, during the past decade, to the discussion of
its true position, as a marked and well-known illustration. In hexapods
the common earwig and flea are familiar illustrations. These osculant or
aberrant forms occur most among parasitic groups, as the Stylopidae,
Hippoboscidae, Pulicidae, Mallophaga, etc. Probably no hexapod, however, has
more interested entomologists than _Platypsyllus castoris_ Ritsema, a
parasite of the beaver. I cannot better illustrate the diversity of
opinion respecting its true position in zoology than by giving an epitome
of the more important literature upon it.
[12] Read at the meeting of the National Academy of Sciences, April 20,
1888.
J. Ritsema, in _Petites Nouvelles Entomologiques_ for September 15, 1869,
described the species as _Platypsyllus castoris_. He found it on some
American beavers (_Castor canadensis_) in the zoological garden of
Rotterdam. He considered it to "undoubtedly" belong to the Suctoria of De
Geer, and to form a new genus of Pulicidae.
In the same year, in the _Tijdschrift voor Entomologie_, 2d ser., vol. v.,
p. 185 (which I have not seen), the same author publishes what is
apparently a redescription of the insect. He gives his views more fully as
to its systematic position, considering that it belongs to the
Aphaniptera, and is equivalent to the Pulicidae.
In the same year, Prof. J. O. Westwood (having previously read a
description of the species, November 9, 1868, before the Ashmolean Society
of Oxford) published in the _Entomologist's Monthly Magazine_, vol. vi.,
October, 1869, pp. 118-119, a full characterization of the insect under
the name of _Platypsyllus castorinus_. A new order, _Achreioptera_, is
established upon the species, which he very aptly likens, in general
appearance, to a cross between a flattened flea and a diminutive
cockroach. "The abnormal economy of the insect, its remarkable structure,
the apparent want of mandibles, our ignorance of its transformations, and
the possibility that the creature may be homomorphous in the larva and
pupa states," are the reasons assigned for establishing the new order, and
here Prof. Westwood is perfectly consistent, as in his famous
"Introduction to the Classification of Insects" the Forficulidae are placed
in the order Euplexoptera; the Thripidae in the order Thysanoptera; the
Phryganeidae in the order Thrichoptera; the Stylopidae in the order
Strepsiptera; and the Pulicidae in the order Aphaniptera.
In 1872, Dr. J. L. Le Conte published his paper "On _Platypsyllidae_, a New
Family of Coleoptera" (Proc. Zool. Soc. of London for 1872, pp. 779-804,
pl. lxviii.), in which he shows that _Platypsylla_ is undoubtedly
coleopterous and cannot possibly be referred to the Aphaniptera. Careful
descriptions and figures of anatomical details are given, and he finds
that its affinities are very composite, but in the direction of the
Adephagous and Clavicorn series. Its most convenient place is shown to be
between the _Hydrophilidae_ and _Leptinidae_. There seems to be no good
reason why the name _Platypsyllus_ is here changed to _Platypsylla_, a
spelling adopted by most subsequent American writers.
In 1874, Prof. Westwood, in the "_Thesaurus Entomologicus Oxoniensis_"
(Oxford, 1874), p. 194, pl. xxxvii., gives figures with details; reprints
his previous diagnosis, and maintains his previous course in erecting a
new order for the insect, without giving any additional reasons.
In 1880, P. Megnin, in "Les Parasites et les maladies parasitaires," etc.,
Paris, 1880, gives (pp. 66-67) a description of the family
"Platypsyllines" without expressing an opinion concerning the systematic
position. He also describes and figures the species.
In 1882, Dr. Geo. H. Horn (Trans. Amer. Ent. Soc., x., 1882-83; Monthly
Proc., Feb. 10, 1882, p. ii.) exhibited drawings illustrating the anatomy
of _Platypsylla_ and _Leptinus_, and showed that a close relationship
exists between these genera. Later, in his "Notes on Some Little Known
Genera and Species of Coleoptera" (Trans. Amer. Ent. Soc., x., 1882-83,
pp. 113-126, pl. v., 114-116), he reviews the characters, and explains and
illustrates the anatomical details. The differences he points out between
his observations and those of Le Conte are more particularly in the
mandibles. In connection with this paper he also describes and illustrates
the structure of Leptinillus, which he separates from Leptinus, and
demonstrates their close relationship with Platypsyllus.
In 1883, Le Conte and Horn, in their "Classification of the Coleoptera of
North America" (Washington, Smithsonian Institution, 1883), give (pp.
13-15) a full description of the family characters, a little modified from
Le Conte's first description, but sustaining his views on the systematic
position of _Platypsyllidae_.
In 1883, Alphonse Bonhoure (Ann. Soc. de France, 1883; Bull, des Seances,
p. cxxvi.) exhibited drawings and specimens of _Platypsyllus castoris_
found in the _Departement des Bouches du Rhone_.
In 1884, Edm. Reitter, in "_Platypsylla castoris_ Rits. als Vertreter
einer neuer europaischen Coleopteren-Familie" (Wiener entom. Zeit. iii.,
1884, pp. 19-21) gives a lengthy description of the species with special
regard to the sexual differences. He shows that the European insect is not
specifically distinct from the American form, but he does not express an
opinion on the position of the family among the Coleoptera.
In the same year, Bonhoure (Ann. Soc. Ent. de France, 1884, pp. 143-153)
more fully records its discovery on _Castor fiber_ taken in the
Petit-Rhone. It is a question whether this European beaver, now quite
rare, is distinct from ours. He gives a very good review of the subject,
with a plate of the most important details, after Horn, and he fully
indorses the coleopterological position of the insect.
In the same year Ritsema (_Tijdschrift voor Entomologie_, 1883-84,
lxxxvi.) refers to Bonhoure's discovery of _Platypsylla_ in France, and
corrects Reitter in some unimportant details.
In 1885, Reitter, in "_Coleopterologische Notizen_" xiii. (Wiener
entomolog. Zeit., vol. iv., 1885, p. 274), answers Ritsema's criticism.
In the same year, Dr. Friederich Brauer, in his masterly
"Systematisch-zoologische Studien" (Sitzh. der Kais. Akad. der Wissensch.,
xci., p. 364), speaks of the relationship in the thoracic characters
between Mallophaga and Coleoptera as illustrated by Platypsyllus, by
inference admitting the coleopterous nature of the latter, but recognizing
that it has mallophagous affinities.
In 1886, H. J. Kolbe, in his "Ueber die Stellung von Platypsyllus im
System" (Berlin entom. Zeitsch., xxx., 1886, pp. 103-105), discusses the
subject, without any new evidence, however. He concludes that most of its
characteristics relate it to the Corrodentia, and particularly to the
sub-order Mallophaga, in which it has its closest kinship in Liotheidae.
The remarkable tripartite mentum he thinks should not be compared with the
bipartite mentum of Leptinus, and calls attention to the fact that in
Ancistrona in Mallophaga it is also trilobed.
The above are the more important papers on the subject, though the insect
has been referred by other authors to both Neuroptera and Orthoptera.