ART. 11 SOME BUEGESS SHALE FOSSILS — HUTCHINSON 21 



in all adult living Onychophora. The anterodorsal region of the brain 

 of the Polychaets, bearing eyes, tentacles, nuchal organ, etc., is of mul- 

 tiple origin, though strictly comparable with the same region in the 

 Onychophora. It is still a matter of debate whether its various com- 

 ponents are to be regarded as somites or as presegmental ; still less 

 can we determine whether the frontal organs of the embryos of 

 Peripatidae are serially homologous with succeeding appendages. 

 A discussion of the apparent segmentation of this region is outside 

 the scope of the present paper for which purpose it seems best to 

 consider only the appendages, no other indications of segmentation 

 being preserved in the fossils under consideration.^ If we are to 

 give any weight whatever to a phylogenetic interpretation of embry- 

 ology, we may conclude that at some stage in their ancestry the 

 modern Onychophora passed through a stage in which the head bore 

 a pair of postoral antennae, and that these were preceded by some 

 sort of tentacle or frontal organ and succeeded by a series of uniform 

 trunk legs bearing claws and crural glands as in the modern forms. 



The following speculative interpretation of the head of Aysheaia 

 fits well into the scheme derived from the embryological findings. 

 It has already been indicated that the branched appendage, as shown 

 in the laterally compressed specimen (&), lies at a rather higher 

 level than the succeeding members of the series of appendages. 

 This fact alone tends to indicate that it is homologous with the 

 antenna of the modern Onychophora in spite of its less anterior and 

 clearly postoral position. Like the antennae, moreover, it is struc- 

 turally dissimilar to the succeeding appendanges and lacks claws. It 

 is, therefore, within the limits of justifiable speculation to equate 

 the two organs. Posterior to the branched appendage of Aysheaia 

 lies a uniform series of legs. It has, however, been pointed out 

 that such evidence as is available strongly suggests that the two 

 appendages succeeding the antenna of modern Onychophora were 

 at some stage similar to the other legs. In front of the branched 

 appendages in specimen {a) lies a small papilliform projection 

 which was probably tactile or trophic. If the above speculation is 

 sound we can regard this as homologous with the frontal organ of 

 the embryo of the Peripatidae. It is to be noted that there is every 

 probability in favour of an Onychophoran with a terminal mouth 

 having a very uncephalized anterior end ; moreover, the segments are 

 relatively long throughout Aysheaia, so that every opportunity is 



3 Through the kindness of Prof. Alexander Petrunkevitch I have been able to examine 

 his very fine collection of serial sections of the heads of West Indian specits of Peripatus. 

 The brain in these forms seems to be substantially like that of Pciipatopsis capensis 

 (Grube) described by Holmgren, and I can add nothing of importance to the conclusions 

 Of the latter worker. 



