GENERAL CONSIDERATIONS. 213 



mandibles of the Insecta, but this condition in Peripatus recalls a 

 similar feature in the Crustacea, in which the ganglia of the second 

 antennae are incorporated in the brain. The second antennae of 

 the Crustacea may thus better be compared with the jaws of 

 Peripatus. Then, however, the question arises, whether a segment 

 has not been lost in the Insecta. This point can only be fully 

 discussed later on (ch. xxviii.). Our view of the antenna-bearing 

 segment, and of its relation to that of the Crustacea or of the air- 

 breathing Arthropoda on the one hand, and to the cephalic segment 

 of the Annelida on the other, has already been stated (p. 186), and 

 to this we must refer the reader. We must, however, point out 

 that, in the transformation of the anterior limbs into mouth-parts, 

 Peripatus approaches the Arthropoda and is removed from the 

 Annelida, in which the jaws are mere cuticular developments of 

 the stomodaeum. 



There can be no doubt that, by the development of limbs armed 

 with claws, Peripatus is in advance of the Annelida ; on the 

 other hand, the limbs are without the segmentation characteristic 

 of the Arthropoda ; the lateral position of the feet also seems a more 

 primitive character inclining towards the Annelida, this character, 

 together with the homonomous segmentation of the body, giving 

 Peripatus a worm-like appearance. Another point of resemblance 

 to the Annelida is found in the crural glands, which have no doubt 

 rightly been traced back to the glandular sacs (setiparous glands) 

 of the Annelidan parapodia (Balfour). The crural glands are 

 found again in the higher Tracheata, although in these transformed 

 nephridia (coxal glands) have repeatedly been held to be the honio- 

 logues of the crural glands of Peripatus. The passage of the 

 primitive segments into the limbs, which is so characteristic of 

 Peripatus, recurs, though not to such a great extent, in the 

 Myriopoda, the lower Insects, and the Arachnida. 



When the mesoderm-bands first appear and break up into 

 segments, their wide extension brings about a great resemblance 

 between the embryo of Peripatus and the Annelida, though it 

 must not be forgotten that this similarity is greatest just in the 

 species in which the yolk is most reduced, and which we must 

 therefore assume show a derived condition (African and American 

 species).* With regard to the development of the mesoderm, 

 Peripatus shows, on the whole, a greater resemblance to the 

 Arthropoda, if the musculature and the segmental repetition of 



* [See footnote, p. 165. — Ed.] 



