THE GONOSOME. 



37 



are seen to be disposed upon each side of a hollow longitudinal septum {c). Tiiis septum consists 

 of a diverticulum of the cndoderm of the radiating canal ; it admits into its interior the fluid which 

 circulates in the radiating canal, and is plainly homologous with a laterally extended and flattened 

 spadix ; while the generative elements are externally confined by an ectodermal covering, which 

 is in the same way the homologue of the perigonium in an ordinary sporosac, but here flattened 

 out like the spadix, in accordance with the ribbon-shaped form of the gono[)liore. 



Fig. 11. 



Fig. 12. 



Portion of the ribbon-shaped sporosac, much en- 

 larged in a female specimen of Tima Baird'd, 



a, a, a, radiating canal ; b, b, b, sporosac ; c, ectoderm; 

 d, endoderm; e, cavity of the spadix ; e', e', distal edge of 

 the spadix, seen through the ectodermal layer ; /, ova. 



Medusa ( Tima Bairdii), a blastocheme of unknown trophosome, 

 showing the convoluted and ribbon-shaped sporosacs along the 

 course of the radiating canals. 



The blastocheme is thus essentially a free non-sexual medusa, which, like the blastostyle, 

 gives origin to sexual buds, but wiiich, unlike the blastostyle, is endowed with the locomotive 

 powers of a medusa, so that it carries those buds from place to place by the contractions of an 

 umbrella. 



In the account here given of the blastocheme, I have confined this term to such medusae as 

 develop distinct sexual buds upon the gastro-vascular canals. In some of those medusae, 

 however, in which the sexual elements are produced in the walls of the manubrium, we find the 

 portions of the walls w-hich give origin to the ova or spermatozoa more or less difl'ercntiated from 

 the general walls of the manubrium, and presenting a lobulated appearance, which might easily 

 lead to the belief that the manubrium emitted from its sides true sexual buds. I am not, 

 however, prepared to place any of these cases in the same category with the blastocheme. 



