ON THE OVIPAROUS SPKOIES OP ONYCHOPHORA. 379 



the chorion is very strongly developed and has an elaborate 

 structure. It is formed while the egg is passing down the 

 oviductj evidently partly, if not entirely, by a secretion of the 

 walls of the latter, and is, I believe, homologous with the 

 coating of the spermatophore in the male and with the 

 chorion of the uterine egg in P. novas-zealandiae. 



The structure and mode of formation of the chorion are, 

 however, extremely difficult to understand, and I propose to 

 describe it sepai-ately in the two species in which it has beeu 

 observed. 



In 0. oviparus I have observed three well-marked stages 

 in the development of the chorion, which we may term A, B, 

 and C, respectively. 



Stage A. — This stage I have observed only in a specimen 

 from Cooran, Queensland, collected by Professor W. Baldwin 

 Spencer, in October, 1891. In surface view the chorion 

 exhibits a finely and uniformly punctate appearance, except 

 over certain areas which appear clear and transparent 

 (fig. 18). These clear areas are rounded in outline, and 

 distributed at fairly regular intervals over the chorion. In 

 a specimen stained with eosin the clear areas seem to be 

 crossed by very irregular networks of darkly stained threads, 

 and in many of them a darkly stained nucleus-like body is 

 visible (fig. 18). Possibly each ol: the clear areas marks 

 the position of an epithelial cell, derived either from the 

 ovarian follicle or from the wall of the oviduct, but the 

 scanty material at my disposal has not enabled me to decide 

 this question. In optical section (fig. 19) the chorion is seen 

 to be very thick (about 0"02 mm.), except in places corre- 

 sponding to the clear areas, where it thins out very greatly. 

 It is also seen to be marked by fine vertical strise, possibly 

 canaliculi, whose cross sections undoubtedly give rise to the 

 punctate appearance seen in surface view. The fact that this 

 specimen was collected in the spring probably accounts for 

 the incomplete development of the chorion ; the eggs would 

 probably not be deposited till much later in the season, as 

 I shall show subsequently. 



