TIMA FORMOSA L. AGASSIZ 31 



nematocysts. The latter are spindle-shaped and immense in 

 number. 



Muscular system. As already stated the muscular sys- 

 tem of Tima consists of subepithelial striated and non-striated 

 fibres. To the former belong the circular fibres of the sub- 

 umbrella, of the peduncle and of the subumbral side of the velum, 

 to the latter the radial fibres of the subumbrella and the longitu- 

 dinal fibres of the peduncle, manubrium and tentacles. In the 

 tentacles the longitudinal fibres are found only in the shape of 

 one strand in their velar side, while circular fibres are entirely 

 absent. There are no endodermal muscle fibres in Hydro- 

 medusae. 



Nervous system. The nervous system consists of a 

 subepithelial network of ganglionic cells and fibres in the sub- 

 umbrella, peduncle and manubrium, and of two rings in the base 

 of the velum. The rings are usually termed the central nervous 

 system. They too are composed of ganglionic cells and fibres. 

 One ring is subumbral in position, the other exumbral ; the rings 

 are concentric and are separated from each other by the meso- 

 gloea of the velum. The subumbral ring innervates the circular 

 muscles of the velum. The exumbral ring is the heavier of the 

 two and innervates the tentacles, the marginal sense organs and 

 sensory cells. The two rings are connected with each other by 

 fibres. 



Statocysts. Tima formosa has one hundred twenty-eight 

 simple statocysts along its margin, alternating with the 

 protuberances and tentacles. The statocysts are more or less 

 round bodies of very small size. They consist of ectodermal 

 cells and each statocyst contains from fifteen to twenty con- 

 cretions arranged in a hemisphere. The function of the stato- 

 cysts is that of controlling the equilibrium of the body. 



Reproductive system. The reproductive organs of Tima 

 are simple gonads. They are nothing but specialized ectodermal 

 cells of the subumbrella and peduncle in the region of the radial 

 canals. They appear as four long sinusoid bands. The repro- 



