THE PYCNOQONIDS. 35 



habitat, and in general, what we may suppose to have happened, 

 was a decrease in the size and an increase in the number of eggs, 

 with the resulting early development of the free larva that we 

 find to-day. This larva represents the more anterior segments of 

 the adult, viz. that part containing the proboscis, the oesophagus, 

 the eyes, the chelae, and two post-oral appendages. Behind this 

 is an undeveloped part, which slowly grows in length as the 

 animal increases in size. The anus belongs to the last segment, 

 and does not appear until that segment is wholly or in part 

 developed. 



If the Arachnids have come from Annelid ancestors with 

 many segments, we have a clue to the slight resemblance between 

 the Pantopod and the Trochophore. The former represents the 

 most anterior segments of the adult Sea-Spiders, and therefore 

 to some extent the anterior segments of the Annelids or of the 

 Trochophore. But at no time in the ontogeny of the Pycnogo- 

 nids have Trochophore and Pantopod-larva been transformed 

 the one into the other, as Dohrn believes. 



Such seems to me the more probable view of the meaning of 

 the Pantopod-larva. This belief has grown out of my work on 

 the embryology of the group, and whether future work supports 

 or disproves such an hypothesis, it is hoped it may be useful, if 

 only as furnishing another point of view for looking at thephylo- 

 geny of the Pycnogonids, or may lead to a more complete study 

 of the embryology of the group. 



