CABEREA 3 8 S 



developed distal lobe, are present on them, and neither the projection from the outer 

 margin of the opesia nor that at the base of the stalk of the scutum is present. The 

 cryptocyst is narrow and the vibracula small. On succeeding zooecia, frontal avicularia 

 appear, the spines decrease in number, the cryptocyst becomes wider proximally and 

 more granular, the scutum becomes blunter distally and meets a lobe from the opposite 

 edge of the opesia, and the vibracula increase in size, until the typical adult charac- 

 teristics are attained. 



From Marion Island there are several young colonies which have not advanced far 

 enough to show the characteristics of the species but agree so closely with the corre- 

 sponding parts of the more advanced colonies that they are identified with fair certainty. 

 The young colony from St. TN 339 (Ross Sea), shown in Fig. 23 B, C, is similar. In it 

 the ancestrula was lightly attached by a membranous vesicle as well as by a pair of root- 

 lets springing from the bases of the two first zooecia. The vesicle evidently represents 

 the primary attachment by which the ancestrula was fixed before the rootlets developed, 

 and no doubt other ancestrulae, now slung by rootlets, were originally attached in the 

 same way. In some of them the remains of the vesicle can be seen. 



A few ancestrulae which have not yet given rise to a whole zooecium have also been 

 identified with C. darwinii on the strength of their agreement in shape, and the presence 

 of less dubious specimens from the same stations. It is interesting to see that the first 

 pair of rootlets, and the vibracula belonging to the first two zooecia, may be fully formed 

 while the buds of the zooecia are still at a very rudimentary stage. On the other hand, 

 one of the specimens with a fully formed first zooecium has only one vibraculum. 



The fifteen ancestrulae from Marion Island, Prince Edward Island and South Georgia 

 range in length from 0-34 to 0-42 mm., the average being 0-37 mm. The four ancestrulae 

 from the Ross Sea region are larger, ranging in length from 0-42 to 0-50 mm., average 

 0*46 mm., which suggests that the ancestrulae, like the other zooecia, are larger in the 

 Antarctic. This might perhaps be expected, but more Antarctic ancestrulae would be 

 needed before it could be regarded as established. 



5. Caberea darwinii var. occlusa var.n. Fig. 22 D. 



Caberea darwinii (part) Busk, 1884, p. 29, pi. xxxii, fig. 6a, b. 



Caberea boryi Hasenbank, 1932, p. 359, text-fig. 28. 

 Station distribution. Not represented in the Discovery collections. 

 Geographical distribution. South Africa (Busk ; Hasenbank). 

 Holotype. Challenger St. 142, 35° 4' S, 18 37' E, 150 fm., 87. 12.9. 132. 



One colony from Challenger St. 142 has already been described among the specimens 

 of C. darwinii (p. 379), but two others (87 . 12 . 9 . 132, 138) appear to represent a distinct 

 variety. In them the cryptocyst on the outer distal side of the opesia is expanded in 

 such a way that three-quarters of the proximal border of the operculum is in contact 

 with the distal edge of the cryptocyst, the remaining quarter being connected with 

 the small process from the other side of the opesia and with the very narrow distal 

 lobe of the scutum (Fig. 22 D). The inner distal spine is rather constantly present. 



