CHAPTER X. 

 POLYZOA 1 . 



ENTOPROCTA. 



THE development of the larvae of Pedicellina is known from 

 the researches of Hatschek (No. 299) far more completely than 

 that of Loxosoma, though it does not apparently differ from it 

 except in certain details. In both the known Entoproctous 

 genera the segmentation is regular or nearly so, though Hatschek 

 believes that he has detected in Pedicellina a slight difference 

 between the two first segmentation spheres, and regards them as 

 constituting the animal and vegetative poles of the embryo. The 

 segmentation in Pedicellina, to which genus alone the remainder 

 of the description applies, results in the formation of a single- 

 layered blastosphere, with a small segmentation cavity, in which 

 the animal and vegetative poles can readily be distinguished 

 owing to the smaller size of the cells at the animal pole. 



The hypoblast cells and the vegetative 2 pole become invagi- 



1 The classification of the Polyzoa adopted in this chapter is shewn in the sub- 

 joined table : 



I. Entoprocta. 

 II. Ectoprocta. 



fa. Chilostomata. 

 i. GYMNOI^EMATA 16. Ctenostomata. 



v. Cyclostomata. 

 i. PHYLACTOL^MATA. 

 3. PODOSTOMATA (Rhabdopleura). 



2 The succeeding statements about the gastrula are derived from Hatschek. 

 According to Salensky a segmentation cavity is not present, and the hypoblast would 

 seem to be formed by delamination or epibole. Barrois finds a gastrula in both 

 Loxosoma and Pedicellina, but gives no details. Uljanin finds a segmentation cavity 

 in Pedicellina, and Schmidt would appear to have observed a gastrula stage in 

 Loxosoma. None of the accounts we have can be compared in fulness of detail to 

 that of Hatschek. 



