144 University of California Publications. [zoology. 



The protection and nourishment afforded the embryo of Crista 

 are typical of the Cyclostomata, and are paralleled to a certain extent 

 among the Ctenostomata and the Phylactolasmata. According 

 to Prouho, the. Ctenostonies are, as a rule, viviparous, the different 

 genera showing degrees of this condition varying from the primi- 

 tive state exhibited by Alcyonidiwm duplex, where the young are 

 sheltered during a portion of their development only, to that 

 found in Pherusa tubulosa, for example, where several embryos 

 develop in the tentacle sheath of a degenerated polypide. Joliet 

 ("77) , who studied the living animal, has given the most detailed 

 account of the process. He shows that in Valkeria cuscuta, 

 another Ctenostome, upon the degeneration of a polypide there 

 appears in the zocecium both an egg and a new bud. The latter 

 grows into an immature polypide but develops a tentacle sheath 

 and the muscles belonging thereto. The small polypide soon 

 degenerates while into the newly formed tentacle sheath the egg 

 finds its way, and there develops into an embryo and ultimately 

 into a larva. In both Crisia and Valkeria the development of 

 the embryo is accompanied by the destruction of the polypide, 

 and in both the embryo develops inside of the tentacle sheath 

 newly produced to receive it, in the one case in a highly modified 

 zocecium, in the other, in an old unmodified one. 



The developmental processes of the Phylactolaemata as exhib- 

 ited by Plumate.Ua show a closer resemblance in some respects to 

 those of Crisia. According to Braem an ovary and a bud develop 

 simultaneously on the body wall, the bud differing from an ordi- 

 nary polypide bud in the possession of a high columnar layer and 

 a flattened mesodermal layer. One of the cells of the ovary grows 

 larger than the others, and partly by increase in its size, partly 

 by pressure from behind, it approaches the side of the bud, pushes 

 through it and becomes enveloped by it. This bud which accord- 

 ing to Braem, Kraepelin ('93) and others is homologous with an 

 ordinary polypide bud, now performs the function of a broodsac 

 or ooecium, and shelters the embryo until it develops into a 

 larva. The origin of the ovary of Plumatella appears to 

 be similar to that in Crisia in its independence of a 

 polypide. The suggestion of Braem, however, in regard to the 

 relation sustained by the ovary of Plumatella and the bud which 



