No. 609] SHORTER ARTICLES AND DISCUSSION 



573 



cloaca, carryinfr its wall before it. thus becoming inclosed in an 

 epithelial capsule. This capsule is soon cast off and, in its place, 

 a placenta is formed which, communicatinjr with the blood- 

 channels of tlie zooid, nourishes the growinf? embryo until l)irth. 

 While the embryo projects into the cloaca it is not, at first, ex- 

 posed to tlie water, but is enclosed by an epithelial capsule and, 

 after its disappearance, by an embryo sac resembling somewhat 

 the amnion of vertel)rates. Later, but still while very young, 

 this sac is distended and finally broken by the growing embryo 

 and from then until birth, the embryo is directly exposed to the 



of the i)lacenta to the walls of tlie cloaca. After the embryo has 

 reached maturity and made its escai)e into tli(> water, the testis 

 matures and the zooid becomes a fully (hn-(M()p(Ml male. Vir- 

 tually, then, the mother sali)a uives i-ise. by huddina', to its sons; 

 and each son sei'ves first as a depository tor mw of its mother's 

 unfertilized eggs, then as a livimr iii<Mil)at(>i' wiiliin which its 

 mother's daughter is IioummI ;ni,| r>';itvd. ;iiul l.-iNtly ;is a father. 



