COMPARISON WITH HEAD OF ANNELIDS. 



327 



in Annelids and any group of Arthropods remains, for the 

 present, undetermined. 



On another debated point the embryological evidence obtained 

 in recent years also throws light. The anterior antennae of the 

 lower Crustacea, and the antennae of Peripatus, Myriapoda and 

 Insecta differ markedly from the appendages of other segments 

 in their simple, many- jointed and generally uniramous character, 

 and these characters in the adults are emphasized by the con- 

 stantly uniramous condition of the first antennae in the Nauplius 

 larva of Crustacea. The question has arisen Have we not in 

 these appendages the homologues of the paired tentacles of the 

 prestomium of Annelids ? 



In the case of Peripatus it is possible that we have, but in the 

 other groups the answer of embryology is in the negative. In 



FIG. 230. Peripatus capensis (after Sedgwick). 



each they are innervated from the mesocerebrum, and there is 

 evidence in Myriapoda that there has existed at least one seg- 

 ment anterior to that which bears them. Notwithstanding the 

 peculiar character of the first antennae we have to conclude 

 that they, like the other appendages of the head, were origin- 

 ally postoral limbs. 



The facts that in Peripatus the antennae are the appendages 

 of the first somite, and therefore, presumably, the representa- 

 tives of the transitory preantennae of the Myriapoda, and that 

 the mandibles belong to the second segment, would seem to 

 place this remarkable genus in a category apart from the other 

 groups of the Arthropoda. 



As the mouth moves backwards the segments originally 

 postoral become preoral, and their ganglia, fusing together, 

 form the brain or supraoesophageal gangliom'c mass of the adult. 



