On Two New Species of Polyplax (Anoplura) from Egypt

Summary. An examination of the immature forms in these three species of Polyplax reveals that the metamorphosis in all three consists probably of at least three distinct stages, although there may be more than two moults. The differences between Stages II. and III. are slight. In the first stage the louse is very soft and delicate for the most part, although even thus early the mouth‐parts, thorax, and legs are well chitinised. On the abdomen segmentation is absent except at the end, and sclerites are absent in all three stages, although in P. oxyrrhynchus and P. spinulosa minute pleurites appear in Stage II., and in Stage III. of P. brachyrrhynchus also there are present weak pleurites of indefinite outline. The spiracles are large. In the last stage the head and thorax closely resemble the adult. In all three stages the chætotaxy of the head and thorax is almost identical with that of the imago. The abdominal chætotaxy and the abdomen itself, however, undergo a very considerable metamorphosis at the last ecdysis into the imago. The metamorphosis of all three shows that there is a tendency for the hairs to develop from behind forwards, inasmuch as the terminal pleuræ develop hairs while the rest are still bare, and in P. oxyrrhynchus and P. spinulosa the sterna are at first also bare except in the last segment. Two hairs on each tergum and sternum is invariably the number if hairs are present at all. Some of these early stages may represent stages in the phylogeny of the group, and in this connection it is suggestive to recall that the Anopluran genus Linognathus is characterized by the large size of its spiracles and the absence of abdominal plates, just as Polyplax is characterized by the small size of the spiracles and the presence of the plates, so that in future it may be convenient to speak of the larva of Polyplax as the “Linognathus larva.” The larva of P. brachyrrhynchus described above recalls in particular such species as Linognathus breviceps Piaget, L. gazella Mjöberg, L. limnotragi Cummings, L. africanus Kell. & P., and L. caviœ‐capensis (Pallas), in which there is on each pleura of the 3rd abdominal segment an elongate bristle and on the pleuræ of the 7th and 8th two long bristles. The chætotaxy of L. caviœ‐capensis (see figs. 2 & 3, Bulletin of Entomological Research, iv. May 1913, pp. 38 & 39) bears a close resemblance to that of the Polyplax larvæ. Some later work further reveals the fact that a somewhat similar plan of abdominal chætotaxy exists also in the larvæ of at least two species of Linognathus in which the imaginal chætotaxy is more complex. This general plan of chætotaxy, therefore, is perhaps a primitive one in the Anoplura, and Linognathus is perhaps a more primitive genus than Polyplax , and perhaps the most primitive of all the Anopluran genera, an hypothesis which, however, cannot be supported by reference to the systematic position of the host‐species, Linognathus occurring with Hœmatopinus on Ungulates such as the Antelope, Capra and Ovis , and also on the Dog. It would be interesting to know whether Linognathoid types of a, more primitive character than any Anoplura hitherto known remain to be discovered on the primitive Insectivora and other ancient mammalian groups. Hitherto, Anoplura have not been found on Monotremes and Marsupials. It should be remembered that L. caviœ‐capensis is a parasite of the Cape Hyrax—a member of a very isolated group.