14 AUGUSTA ÄRNBÄCK-CHRISTIE-LINDE, NORTHERN AND ARCTIC INVERTEBRATES. 



the right side being fairly well developed. The testes are situated on the ventral side 

 behind the ovaries; they are not quite on a level with each other, the one on the 

 right side being situated farther back than the one on the left. The outer side of 



the testis is strongly convex, showing a large number of 

 lobes of rounded form, all crowded together, which gives 

 a mulberry-like aspect to the gland. On the inner (mesial) 

 surface it is flattened and even and is without lobes. The 

 vas deferens is short, rather widel} 7 projecting from the 

 dorsal börder of the testis and opening into the peri- 

 branchial cavity (ef. Pl. 1, fig. 10). 



The female organs are represented by one-egg ovaries 

 of varying number, which is not always the same on either 



Text-fig. 6. Bdtrylluaschloeseri Pallas. of the two sides - Tn fi g- 5 there are two on each side > 



section through an ovary. x i ni. ec. m #„ 7 there are four on the left side and one on the 



Ectoderm. /. Outer follicle. o. Ovum. _ ° 



od. oviduet. p. Outer waii of the right; in some individuals there are up to six ovaries on 



peribranchial cavity. , . . , i • 1 • , 1 1 , 1 1 ti 



the one side, which is the largest number observea nere. 

 They are arranged in varying ways. In the individuals figured they are in a row 

 alongside the body, but quite as often they are found irregularly scattered though 

 always crowded together and forming a group on each side of the body. In the young 

 zooids figured — the individual illustrated in fig. 7 measures about 1,1 mm. in length 

 — the ovaries are large and of about the same size. They are each enclosed in 

 rounded dilatations of the body-vvall. Apart from the peculiar shape and position 

 of those ovaries one is struck by the vesicle-like struetures representing the oviduets. 

 They project from a point on the mesial side of the globular ovary and are pressed 

 into concavities of the outer peribranchial wall, which forms as it were capsules sur- 

 rounding them. 



Text-fig. 6 represents a transverse section made through a one-egg ovary 

 in Botryllus schlosseri. As may be seen on the figure the ovary lies in the 

 mesoderm and is enclosed by the highly dilated outer body-wall. As is the case in 

 Metrocarpa, it is composed of follicle, oviduet and one egg, which, in this stage, is 

 almost mature. The outer and the inner follicles are differentiated, each being repre- 

 sented on the figure by a line; test cells are easily distinguished within the inner follicle. 

 The oviduet is compressed lengthways as in Metrocarpa, and its wall lies close to the 

 bottom of the concavity of the outer peribranchial wall towards which it has been 

 pressed (ef. text-fig. 6). 



Stage III (Pl. 1, fig. 8. Text-fig. 7). The figures illustrating this stage show 

 part of the reproduetive apparatus of a full-grown zooid. The testes are large and 

 fully developed. The ovaries are not, as is usually the case, in a uniform stage of 

 development. The last one in the row on the left side in this individual is only a little 

 more advanced in development than in the above stage, and is therefore of special 

 interest. The egg is almost mature, as in stage II, and the outer follicle is in process 

 of bursting (text-fig. 7). The vesicle-like oviduet has greatly increased in size and 

 projects more deeply into the concavity formed in the outer peribranchial wall. The 



