2G6 DB J. H. ASHWORTH AND DR JAMES RITCHIE ON THE 



an axial spadix, is radially symmetrical, a symmetry which it retains until the 

 formation of the tentacle. 



We have no examples intermediate between that just described and the free 

 sporosac (fig. 10), but no doubt the male sporosac becomes detached from the 

 blastostyle in the same manner as the female. Like the latter, it is clothed with 

 long cilia, as also is the tentacle, which comes to lie in line with the long axis of the 

 sporosac ; and probably the male sporosac, like the female, swims with the tentacle 

 directed anteriorly. 



In shape the male sporosac is readily distinguishable from the female, since it is 

 elongate oval — the female being sub-spherical, — and is usually a little smaller. The 

 average length (excluding the tentacle) and breadth of twenty male sporosacs are 

 '096 mm. and '064 mm. respectively, the largest being '12 mm. long and '07 mm. 

 broad. The tentacle, when extended, is "04-'06 mm. long. The average length and 

 breadth of twenty female sporosacs are '115 mm. and '1 mm. respectively, the largest 

 being '135 mm. long and "115 mm. broad, and the tentacle is '05-'07 mm. in length 

 when extended. 



The free male sporosac is of simple structure (fig. 10). Externally it is covered 

 with ectoderm composed of regular ciliated cells. The endodermal spadix, which has 

 a central cavity, runs axially from one pole to the other, passing at one end into the 

 solid endoderm of the tentacle and at the other abutting against the ectoderm. The 

 cells of the spadix of most free sporosacs exhibit a degenerate appearance. Between 

 the ectoderm and the spadix lies the cylindrical mass of spermatozoa. We have no 

 observations on the mode of escape of the sperms from the sporosac. 



The Sporosacs of Dicoryne conferta (Alder). 



The characters of the reproductive bodies described in the preceding pages clearly 

 place them in close relationship with the free-swimming sporosac of Dicoryne con- 

 ferta described by Allman (1861 and 1872). The most marked differences lie in the 

 single tentacle of the Neapolitan examples as contrasted with a pair in D. conferta, 

 and in the single oocyte of the former as against the normal pair * in the latter. 

 Allman was content merely to mention the " defined line" along which the sporosac 

 of D. conferta becomes detached, without indicating its origin or nature, and, owing 

 to lack of mature material, the detailed descriptions of later writers have stopped 

 short of the stage at which the tentacles develop. In the hope of correlating more 

 definitely the developmental stages of these remarkable and closely related sporosacs, 

 we have re-examined their development in D. conferta. 



The material examined consists of colonies from (a) Kristineberg, Sweden, lent 

 by Professor Hjalmar Theel from the collections of the Stockholm Museum ; (b) 



* Goette (1907, p. 67) has stated that in young sporosacs of D. conferta there are occasionally three or four 

 oocytes, and sometimes only one ; and Hartlaub (1897, p. 480) has recorded the finding of free-swimming sporosacs 

 of this species, in plankton collections off Heligoland, which possessed three oocytes and the normal two tentacles. 



