TWO NEW LICE. 



Stage III. — Measurements (millimetre scale). 



271 



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 month- 

 parts, thorax, and legs are well chitinised. On the abdomen 

 segmentation is absent except at the end, and selerites are 

 absent in all three stages, although in P. oxyrrhynchus and 

 P. spinulosa minnte 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 chaetotaxy of the head and thorax is 

 almost identical with that of the imago. 



The abdominal chaatotaxy 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 pleurae 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 phylo- 

 geny 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 chai'acterized byt he 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 

 Mjoberg, L. limnotragi Cummings, L. africanus Kell. & P., and 



19* 



