20 AUGUSTA ÄRNBÄCK-CHR1STIE-L1NDE, NORTHERN AND ARCTIC IN VERTEBRATES. 



world. It can be seen from the figure, that one has already reached the cloaca while 

 the other is still in the peribranchial cavity but is in the process of slipping out of 

 *the cup-shaped fold. From the figure of this stage it is apparent that the embryo 

 remains attached to the peribranchial wall by this fold, until it has undergone its 

 full development. 



The zooids examined belong to colonies caught in Jul}', at which time the 

 Botryllidce of the Svvedish coast have generally attained sexual maturity. In colonies 

 collected in August the individuals vary as to the maturity of the sexual products. 

 In some colonies the testes were well developed, the embryos were in late stages of 

 development and enclosed by the cup-shaped folds. In others the testes were much 

 reduced, the embryos had passed into the outer world, though the cup-shaped folds 

 still persisted. 



Reproduction by budding has been observed in the colonies examined. It begins 

 in very early stages. 



Suramary. 



In Bolryllus schlosseri the zooids are hermaphrodite; the male and female or- 

 gans are separated. 



The male and female organs occur together in the very young bud; no proto- 

 gynous arrangement has been observed. 



Both male and female organs occur on both sides of the body. The testis is 

 single on each side. The outer side is strongly convex and lobate; the inner side 

 is even. The vas deferens is short and opens into the peribranchial cavity. 



The female organs consist of several one-egg ovaries of varying number on either 

 side of the body. Each ovary consists of follicle, oviduct and one egg. The ovi- 

 duct is in the form of a fairly large, compressed vesicle that opens into the peri- 

 branchial cavity. 



When mature, the egg passes through the oviduct into the peribranchial cavity, 

 where the fertilization takes place. The embryo is attached to the peribranchial wall 

 by a cup-shaped, placenta-like fold, formed by the outer peribranchial epithelium. 



The outer follicle is thrown off before the egg passes into the peribranchial 

 cavity, and soon commences to degenerate. It may be compared with the corpus 

 luteum in higher Ascidians. 



The embryos remain attached by the cup-shaped folds, until they have become 

 completely developed tailed larvae. 



The cup-shaped folds may be analogous to brood-pouches developed to attach 

 to themselves and to protect, the embryos. No special histological differentiation in- 

 dicating the function of a true placenta has been observed. 



Reproduction by budding commences in early stages and has been observed in 

 most of the colonies examined. 



