HYDROZOA. 39 



ill Many zoologists describe the vesicles as "au- 



ri a t e J ^ ditory organs/' the crystals or other bodies which 



a ra .. : they contain being designated " otolites." But 



*;,'. \ this view of their nature is altogether hypothetical. 



Q ^ v Gregenbaur hints that they, perhaps, constitute an 



**K apparatus of excretion. The pigment-spots may 



^ be regarded with some shade of probability as the 



l he ,; earliest indications of organs of sight, which appear 



1a Ha : among the lower forms of the animal kingdom. 



} pta\ In some ocelli, a spherical, highly refractive cor- 



h puscle has been detected by Gregenbaur within the 



■med- 





mass of pigment. 



m 



Hg^ exists in any of the Hydrozoa. Professor Agassiz 

 ra - describes what he considers as such a system in 



n- the nectocalyces of some of the free swimming 



jj forms. "In Medusae (he writes) the nervous 



^ ' : system consists of a simple cord, of a string of 

 w . ovate cells, forming a ring around the lower 



margin of the animal, extending from one eye- 

 speck to the other, following the circular chymi- 

 miW, ferous tube, and also its vertical branches, round 



)econ the upper portion of which they form another 



circle. The substance of this nervous 



em 



email;, however, is throughout cellular, and strictly so, 



and the cells are ovate. There is no appearance 



hey ocs in any of its parts of true fibres." But the struc- 



^ ture of the tissues here described as nervous is 



jj-. very susceptible of a different interpretation. 



iel M'Crady and Fritz Miiller have also speculated 



m 



sidce. The former naturalist states that, among 

 several species, he has observed a distinct ganglion 

 ^ V in the neighbourhood of each marginal body. 



D 4 



