1882.] 



The Development of Kenilla. 



387 



(13.) The spicules are developed in the interior of cells and are of 

 tAvo kinds, ectodermic and endodermic, which differ widely in form 

 and size. Professor B. K. Emerson has kindly examined them for me 

 with the polariscope, and finds them to consist of a crystalline core, 

 probably of aragonite, surrounded by an amorphous layer and this by 

 a second crystalline layer, the axes of which correspond with those of 

 the core. 



(14.) The ventral chamber becomes closed in front by membranous 

 outgrowths from the septa and body- walls. The dorsal chamber is 

 closed by the forward extension of the fore edge of the peduncular 

 septum, which finally unites with the dorsal wall of the body just 

 anterior to the exhalent zooid (vide infra). 



III. 



(15.) The development of the buds is essentially like that of the 

 axial polyp, but no trace of the peduncular septum is formed and the 

 mesenterial filaments appear in a different sequence, the dorsal pair 

 appearing first and developing most rapidly. 



(16.) The buds which are to form sexual polyps appear always in 

 symmetrically placed pairs, and, in the earlier stages, in a definite 

 sequence. They are arranged in two simple lateral rows, which 

 extend both forwards and backwards by the appearance of new buds 

 npon the axial polyp. The backward extension is, however, limited, 

 whence results the sinus, into which the peduncle is inserted. An- 

 teriorly the two rows of buds extend forwards and downwards until 

 they meet at the ventral side of the axial polyp, which is thus- 

 included within the disk. 



New buds are constantly formed in the angles between older buds, 

 and each lateral bud is in time enclosed by the younger adjacent buds 

 in the same manner as the axial polyp. 



(17.) The ventral sides of the buds are at first directed down- 

 wards, and hence, when the polyps in later stages bend upwards SO' 

 as to assume a vertical direction, the ventral side is turned outwards, 

 away from the centre of the disk. 



(18.) The zooids develop in the same manner as the polyps and are 

 indistinguishable from the latter in their early stages. They are at 

 first single but soon multiply to form clusters, in which the ventral 

 chambers of the zooids are always turned away from the centre of the- 

 group. The law of budding is therefore the same for the zooids and 

 polyps. In rare cases the secondary zooids become in turn centres of 

 multiplication according to the same law. 



The axes of the primary zooids are definitely related to those of 

 the polyps on which they are placed. 



(19.) The "Hauptzooid" of Kolliker is formed at an early stage 

 as a median bud upon the axial polyp, and its function is to discharge 



