ENTOPROCTA. 



569 



The generative organs are continuous with their ducts, and open 

 on the ventral surface between the mouth and anus ; in Pedicellina 

 they open into a kind of brood-pouch in the ventral Avail of the 

 vestibule on the anal side of the ganglion. They are paired glands, 

 and the ducts of the testes open into a vesicula seminalis. Pedi- 

 cellina is hermaphrodite, but the organs of the two sexes do not 

 appear usually to mature at the same time. Loxosoma is dioecious. 



The early stages of development take place in the brood-pouch. 

 The ovum undergoes total cleavage, and an invaginate gastrula with 

 two pole cells is formed. The blastopore remains open in the 



Fro. 454. Development of Pedicellina cchlnata (after Hatschek). a, blastosphere. b and c, 

 later stages in optical section, d, young larva in median optical section, e, free-swimming 

 larva extended. A vestibule ; Af rudiment of the rectum ; Dr apical thickening ; EC 

 ectoderm ; En endoderm ; F h segmentation cavity ; Hd rectum ; Kn dorsal organ ; L liver 

 cells ; Ms mesoderm ; N excretory canal ; Oe oesophagus. 



position of the anus, and the pole cells give rise to two short 

 mesoblastic bands. The embryo leaves the brood -pouch as a 

 trochosphere larva (Fig. 454), with a well-marked velar ring of 

 cilia having the same relation to the mouth and anus that the 

 tentacles have in the adult, an apical thickening of ectoderm (Dr), 

 which carries a tuft of cilia and consists of large glandular cells, 

 and a pit of thickened ectoderm on the anterior side of the dorsal 

 surface (kn) called the dorsal organ. The apical thickening is 

 variously interpreted as a sense organ and an organ for adhering ; 

 the dorsal organ is provided with two pigmented eye -spots in 



