430 DR S. F. HARMER AND DR W. G. .RIDEWOOD ON THE 



levinseni, C. (Demiothecia) gracilis, and C. (D.) sibogw in having a single nerve- 

 tract in the stalk. 



The number of the nerve-tracts in the region in question is no doubt correlated with 

 the way in which the metasomatic muscles are arranged at the point where they pass 

 into the stalk. In C. agglutinans, as in C. levinseni, C. gracilis, and C. sibogie, the 

 layer of metasomatic muscles forms a single fold extending deeply into the cavity of 

 the stalk, round the single nerve-tract, in the region where the stalk is separating 

 from the body. In C. dodecalophus, C. hodgsoni, and C. a'^uatua, in which three nerve- 

 tracts are present, there is, in addition, a pair of muscular folds similarly related to the 

 lateral nerve-tracts. 



BUDS. 



The buds seem to be produced in exceptionally large numbers in the present species, 

 and an examination of the budding disc at the end of the stalk of full-grown zooicls 

 shows that in some cases as many as seven pair of buds are present at the same time. 

 As in other species, the free surface of the disc is of the nature of a sucker for adhering 

 to foreign objects ; the disc is wider than the end of the parental stalk, and the buds 

 develop in pairs in the groove between the stalk and the disc. The youngest buds 

 cannot be said to have any stalks ; they are merely clavate or pyriform outgrowths, 

 which soon show a transverse groove when the proboscis differentiates from the rest of 

 the bud. The stalks of the other buds are remarkably long ; that of one bud with two 

 pairs of arms developing, of the stage shown in text-fig. 5, (', measured 3 '9 mm. ; 

 another of the same stage of development measured 4 '3 mm. 



There is a remarkable uniformity to be noticed in the size of the stalked buds present. 

 The proboscis of a bud in which the first pair of arms are just about to develop, such 

 as is represented in text-fig. 5, A, is not very much smaller than that of a bud in 

 which five pairs of arms can be recognised and it is the proboscis which practically 

 determines the size of the bud. Buds intermediate in size and development between 

 minute stalkless buds just forming from the disc and buds like that shown in text-fig. 

 5, A, are scarce ; and no buds have been found older than that shown in text-fig. 5, 

 F. Indeed, only two buds of the latter stage were discovered. It would seem, there- 

 fore, that buds develop very rapidly up to the time when the first pair of arms make 

 their appearance, and that their subsequent growth is slower. What happens after the 

 stage with five pairs of arms it is impossible to say. The buds of this age seem to be 

 too young to separate off as independent zooids and to leave the colony their alimentary 

 canal is still csecal, and the ten arms have not yet produced any tentacles (text-fig. 5, F) 

 and in some other species of Cephalodiscus (e.g. C. hodgsoni and C. nigrescent, 

 RIDEWOOD, 07 2 ) buds may be found still attached by their stalk to the parent having the 

 full number of arms characteristic of the adult zooids. The absence of old buds in the 

 present material may perhaps be accounted for by some seasonal cause ; or buds may only 

 begin to be produced when the development of the gonads has reached a certain stage. 



(ROY. soc. EDIN. TRANS., VOL. XLIX., 554.) 



