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 

 Loxosoina, 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 forma- 

 tion of a single-layered blastosphere, with a small segmentation 

 cavity, in which the animal and vegetative poles can readily be dis- 

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



The hypoblast cells at the vegetative 2 pole become invaginated in 

 the normal manner (fig. 128 A), the blastopore becomes narrowed 

 to a slit with an antero-posterior direction, i.e. parallel to the line 



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

 table : 



I. Entoprocta. 

 n. Ectoprocta. 



(a. Chilostomata. 



1. GYMNOL^MATA \b. Ctenostomata. 



[c. Cyclostomata. 



2. PHYLACTOLuEMATA. 



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 

 Loxosorna 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 fullness of detail to 

 that of Hatschek. 



