XI POLYZOA 405 



Entoprocta, because only in the case of this group are the larval 

 organs taken over into the adult. 



Now the larva of the Entoprocta, as all investigators admit, is 

 closely related to the Trochophore type of larva. The apical plate is 

 identical in both forms, the corona obviously corresponds to the 

 prototroch, whilst the anal cone of the Entoproct larva may be 

 compared to the post-trochal region of the Trochophore. 



If Lebedinsky is to be trusted (and Hatschek confirms him in 

 some points) the Entoproct larva in reality corresponds to a post- 

 trochophoral stage in Annelid development, since the mesodermal 

 band already exhibits traces of division into three somites. On the 

 other hand the evanescent posterior and lateral ganglia, discovered by 

 Lebedinsky, suggest a comparison with the pleural and visceral 

 gangha of MoUusca, and we have already seen reason to imagine that 

 primitive MoUusca, when they diverged from the Annelidan stock, 

 may have had incipient segmentation represented by two or three 

 somites. The " dorsal organ " may be compared to the cerebral 

 ganglia of the Annelida and MoUusca, which are found a little 

 distance from the apical plate itself 



But starting from an ancestor still retaining the habit of a Trocho- 

 phore though possessing a segmented mesoderm, how are we to inter- 

 pret the metamorphosis ? The closing of the vestibule or atrium and 

 the consequent shutting off for a time of both mouth and anus from 

 the exterior must be a secondary feature, for, during the whole history 

 of the race, mouth and anus must have been continuously functional. 

 Therefore, although it is correct to say that in individual ontogeny the 

 larva fixes itself by the whole of its ventral surface, yet this fixation 

 must represent, in the history of the race, a prae-oral attachment. 



Our Entoprocta, therefore, would be exceedingly primitive 

 Annelida or exceedingly primitive MoUusca, which had become 

 attached just in front of the mouth, and which have, like Cirri- 

 pedia and Crinoidea, undergone such extensive growth of the region 

 of attachment as to rotate the mouth upwards into a more advan- 

 tageous position for catching floating prey. 



The Ectoproct larva in its primitive form, as exemplified by 

 Cyphonautes, is also allied to the Trochophore larva; apical plate 

 and corona have obviously the same significance as in the Entoproct 

 larva. But the Cyphonautes represents the Trochophore in an 

 earlier stage of development than does the Entoproct larva, since it 

 possesses no true mesoderm derived from pole i cells, and has no 

 secondary cerebral gangUon. 



The attempt to compare the pyriform organ to the dorsal organ 

 of the Entoprocta, although boldly essayed by Seeliger, must be 

 pronounced a failure. The pyriform organ, as Kupelwieser has 

 demonstrated, is not a nerve ganglion at all but a peculiar sense 

 organ, and its position within the circle of the corona cannot be 

 compared to that of the dorsal organ of the Entoprocta, which is 

 outside the circle of the corona. 



