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PLATYPSYLLUS— EGG AND ULTIMATE LARVA.* 



By C. V. Riley. 



The egg and the pupa of Platypsyllus are yet unknown. I have for 

 some time endeavored to obtaiu them, and specimens recently received 

 as such gave hope, from the finder's account, that the lacunae in the 

 life-history of the genus might at last be filled. But examination dis- 

 pelled the hope; yet not without adding something to our knowledge 

 of the development of this curious beaver parasite. The only reference 

 to the egg is that contained in Dr. Horn's article in the " Transactions 

 of the American Entomological Society" (Vol. XV, p. 25), where it is 

 stated that the eggs were observed, and that u they are minute objects, 

 not fastened to the hair, as is the case with lice, but plastered firmly to 

 the skin among the thickest hair." This, failing in description, might 

 apply to the egg of any other minute creature, and I have, in fact, some 

 reason for concluding that the objects referred to in the observation 

 were not the eggs of Platypsyllus, but those of quite a different insect. 

 The e^gs, as observed in the oviduct of the female Platypsyllus, are 

 sufficiently uncharacteristic, except as to their flattened formj they 

 are 0.4 mm long and 0.2 mm in broadest diameter, non sculptured, white, 

 broadly ovoid, but much flattened on two sides. The structure indi- 

 cates that they may either be thrust under the scales of the skin or 

 fastened thereto. 



What was sent as the pupa, proves to be a most interesting larval 

 stage and in keeping with the Mallophagous appearance of the beetle. 

 This larval stage might at first sight be characterized as a Mallophagan 

 by even the most careful zoologist. The larva, as hitherto described 

 and figured, even in the largest specimens, whether from Dr. Horn's ma- 

 terial or my own, has always seemed to me inexplicably small as com- 

 pared with the imago, and if the form which I now describe is (and 

 I can believe it nothing else) the final larval form of Platypsyllus, then 

 the larvae hitherto described had not yet gone through their final molt. 

 A glance at the accompanying figures suffices to show the remarkable 

 superficial resemblance to the lice in question, and only when the struct- 

 ure, especially of the leg and mouth-parts is studied, does its Platypsyllus 

 nature appear. The description will also show how greatly it is modi- 

 fied from the earlier larval stages already described. One is justified 

 from the facilities for grasping which it possesses, as from the posi- 

 tion of the head, in inferring this stage quiescent, and in this respect, 

 as well as in the marked deviation from the previous stage, it recalls 

 the pseudo-pupa, or coarctate larva of the Meloids, and of some other 

 parasitic forms. I have but a single specimen and have not been able 

 to clearly make out the spiracles. One can but conjecture as to whether 

 the pupa proper is formed, either partially or wholly, within the skin 



* Reprinted from Entomologica Americana, February, 1890, p. 27. 



