ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 583 



of air spun into the cocoon are produced from the anterior end of the 

 larva itself, probably from the thoracic stigmata. The imprisoned air- 

 bubbles, which are so numerous that they give the whole cocoon a silvery 

 appearance, make tracheal respiration possible throughout the period of 

 pupation — about 25 days. 



There are two kinds of females, a long-winged and a short- or 

 rudimentary-winged type. Transition forms were not found. The 

 long-winged females and the males live in the air, but never go far 

 from water, and quickly die if they are removed from damp air. The 

 short-winged females live entirely in the water, and move awkwardly if 

 taken out of it. The author believes that there is a summer and a 

 winter generation, and that the long-winged females belong exclusively 

 to the latter. The caterpillar passes the winter in a more or less torpid 

 state within its leaf -shelter at the bottom of the pond. 



The short-winged females swim under water with the posterior end 

 at the surface. The stigmata are here very minute, and the author 

 regards this attitude as connected with reproduction rather than with 

 respiration. Copulation takes place at the surface, the female turning 

 round on the dorsal surface when approached by the male. Males may 

 be occasionally dragged under water accidentally, and so have been 

 supposed to enter the water in quest of the females. After copulation 

 the female seeks a suitable twig, lays her eggs, and dies almost at once. 



The last part of the paper contains a discussion of the anatomy of 

 the imagines, with special reference to the difference between the sexes. 

 Many of the secondary sexual characters of the female are shown to be 

 connected with aquatic life : thus the different arrangement of hairs 

 makes the leg of the female an effective swimming organ. The wing 

 stumps are also used in swimming, and the sparseness of the scales on 

 the ventral surface admits of respiration by endosmosis. 



In regard to its systematic position, Acentropus agrees closely with 

 Hydrocampa and other aquatic Pyralidae so far as wing-venation, re- 

 productive organs, and the aquatic life of the larva and pupa are con- 

 cerned, and must therefore be ranked with them. But it stands alone 

 as regards the remarkable modification of the female insect to aquatic 

 life, and it also exhibits a greater degeneration of the mouth-parts than 

 the other Pyralidae. 



7- Prototracheata. 



Distribution and Classification of Onyckophora.* — Adam Sedgwick 

 points out that the known species of Peripatus are referable to seven 

 geographical groups : — (1) those of the neotropical region except Chili, 

 Neo-Peripatus ; (2) those of tropical Africa, Congo-Peripatw ; (?>) 

 Malaya, Eo-Peripatus ; (4) South Africa, Capo-Peripatus ; (5) New 

 Britain. Melano-Peripatus ; (G) Australasia, Austro-Peripatus ; (7) 

 Chili, Chilio-Peripatus. " 



He gives the characters of each of these groups of species, and con- 

 cludes from the survey — (1) that the geographical groups of species are 

 natural zoological groups, the members of which are more closely 

 related to each other than to those of other groups ; and (2) that the 



* Quart. Journ. Micr. Bci.. lii. (1908) pp. 379-40(3 (13 figs.). 



