182 



ONYCHOPHORA. 



The terminal region of the body, up to the time when the adult 

 form is assumed, is almost button-shaped. At its lower side, either 

 in a depression (as in P. Edicardsii) or on a papilla, as in P. capensis, 

 lies the anus. Two slight outgrowths, the anal papillae, which 

 apparently belong to the terminal section, must be regarded as rudi- 

 ments of limbs, and thus indicate a true segment. The limbs 

 themselves have assumed their adult form, being better marked 

 off' from the body, and exhibiting a ringed appearance not unlike 

 segmentation At their free ends the two cuticular chitinous claws 

 arise. The limbs have shifted from their former more ventral 

 position to their final position between the dorsal and the ventral 

 surface. 



With regard to the position of the anus it must be mentioned further that, in 

 consequence of its being found in front of the growing zone, it must be related 

 to a true segment. In various drawings made by v. Kennel and Sedgwick of 

 sections cut through the anal aperture, well developed primitive segments are 

 seen round the terminal region of the intestine. We must then in any case- 

 assume a shifting forward of the anus which originally belonged to the terminal 

 region of the body. The relation of the anus to the segmentation of the body 

 in the adult does not seem satisfactorily settled, nor is it clear whether it 

 subsequently shifts out of the segmented region to the extreme end. 



The development of the anterior region of the body is less simple 



than that of the trunk. 

 Complications arise in the 

 former through two other 

 segments besides the actual 

 cephalic segment being 

 drawn into the formation 

 of the adult head, and 

 through the corresponding 

 modification of the append- 

 ages of these segments. 

 We thus find in Peripetias 

 a state of things already 

 met with in the Crustacea, 

 and still more closely re- 

 sembling conditions found 

 in the Arachnida, Myrio- 

 poda, and Insecta. 

 In the cephalic segment, the rudiments of the antennae have 

 undergone alteration; they have lengthened considerably, and rings 

 like those on the limbs have appeared on them (Fig. 91, at). The 



Fio. 91.— Embryos of P. capensis of different ages 

 (after Sedgwick), at, antenna; aw, eye; /, fold, 

 contributing to the formation of the buccal cavity; 

 k, jaw ; op, oral papilla ; p,-p t i,, first three pairs of 

 limbs. 



