CHAPTEE XVIII. 



ENTOPROCTA. 



The group of the Entoprocta, which, although small, is rendered of 

 interest by the possession of many structural and developmental 

 peculiarities, has hitherto usually been united with the Ectoproc- 

 tous Bryozoa, but it is doubtful if the two should be connected. 

 Of the forms l)elonging to this group, Pedicellina, and nearly 

 allied genera such as PedicelUnopsis, Ascojwdaria (Barcntsia), etc., 

 and, further, Urnatella, form colonies, but in Loxosoma, the buds do 

 not remain connected with the parent, but become detached, so that 

 in this genus only solitary individuals are met with in the adult 

 condition. 



Our knowledge of the embryonic development of Pedicellina, 

 apart from older statements, is principally due to the researches of 

 Hatschek (No. 6), and Harmer (No. 5). The ontogeny of Loxosoma 

 has more recently been described by Harmer (No. 4), whose results 

 agree in essential points with those of Hatschek. 



The eggs of Pedicellina are fertilised while still in the ovary. 

 The embryonic development takes place within the vestibule of the 

 female,* which is transformed into a brood-cavity, the epithelium 

 of which appears to become thickened and glandular for the 

 nourishment of the embryos (Ehlers, No. 2). These are attached 

 to the wall of the brood-cavity by the pointed end of the elongated, 

 pear-shaped egg-envelope (a secretion of the epithelium lining the 

 oviduct). The young larvae, when hatched, still remain in the 

 brood-cavity, and are said to be attached to its wall. 



In the granular and somewhat opaque spherical egg of Pedicellina, 

 enclosed in its vitelline membrane, a somewhat clearer animal pole 

 can be distinguished, near which lies the germinal vesicle. Cleavage 

 is, as a rule, total and unequal, but approaches the equal and regular 



* Pedicellina echinata is hermaphrodite. In other species the sexes appear to 

 be separate. [According to Harmer, Pedicellina is sometimes dioecious and 

 sometimes monoecious, and Loxosoma is perhaps always dioecious. —Ed.] 



