AET. 11 SOME BUEGESS SHAX,E FOSSILS — HUTCHINSON 19 



2. The position of the mouth deserves a passing mention. In the 

 modern Onychophora the mouth lies in a ventrally situated oral cup. 

 The ventral position of the mouth is clearly of considerable value 

 in feeding on solid material, particularly in a terrestrial animal. 

 Terminal mouths may persist or be developed in burrowing forms, 

 but outside the polychaet annelids are uncommon among the higher 

 invertebrates. It is, therefore, of interest that Aysheaia had appar- 

 ently acquired ambulatory limbs while still retaining a terminal 

 mouth. 



Relationship to modern Onychophora. — The strongest evidence in 

 favor of placing Aysheaia in the Onychophora is that afforded by 

 the nature and appearance of the body wall and form and disposi- 

 tion of the appendages. From the modern Onychophora Aysheaia 

 differs in the following ways. 



1. The smaller number of segments in Aysheaia. 



No modern Onychophoran has less than 14 segments bearing 

 clawed legs. This corresponds to a total of 17 segments. In 

 Aysheaia there are 10 segments bearing clawed legs and probably 

 two more, making a total of 12, 



2. The small number of annuli to each segment. 



Aysheaia has 4 annuli of papillae, the modern species all have 

 more than 12. 



3. The large number of claws on the walking legs. 



All modern Onychophora have two claws on each trunk append- 

 age, supported by a complex foot. In Aysheaia there are six claws 

 and the foot was presumably much less elaborate. In the embryo 

 of Peripatus corradoi Camerano, Bouvier (1907, p. 38, fig. 43) figures 

 each claw as covered with a cuticular layer, afterwards shed, bear- 

 ing a number of large denticles. It is highly probable that the claws 

 in adult Onychophora are compound, each representing one of the 

 two groups of three in Aysheaia. 



4. The internal process of the trunk appendages. 



This structure may possibly be homologous with the eversible 

 coxal vesicles of many modern Onychophora, but would seem to lie 

 more distally. The proximal portion is very probably covered by 

 the base of the leg in all the specimens in which the process is shown. 

 The internal process may well have been respiratory; the posses- 

 sion of a soft lobe or spur on the leg would seem more in accordance 

 with an aquatic than a terrestrial habitat, whatever its function. 



5. The terminal mouth. 



This difference has already been discussed. 



6. The structure and arrangement of the anterior appendages. 

 The interpretation of the head of Aysheaia is somewhat specu- 

 lative and is treated at length below. 



