On t/ic Stricture and jDevelopment of I\Iyiiothela. 209 



ajipears to bo but a modification of the tissue ^\■hicll elscwliere 

 forms the zone of clavifonn tissue. 



Ext-ending in a radiatinfj; direction from the convex surface of 

 this rod-like tissue, towards the external surface ef the tentacle, 

 may be seen numerous firm filaments, each of which, making its 

 way among cells of the ectoderm, terminates distally in a very 

 delicate transparent oviform sac, which carries, near its distal 

 end, a minute styliform process. AV^ithin this sac, and com])letely 

 filling it, is an oviform capsule with firm transparent walls, and 

 having immersed in its clear refringent contents a cylindrical 

 cord wound upon itself in two or three coils. Under pressure, 

 the contained cord may be sometimes forced out through the 

 smaller or distal end of the capsule. Xotwithstanding the obvious 

 resemblance of these bodies to thread-cells, their significance is, 

 without doubt, something entirely different. Indeed their re- 

 semblance to the Pacinian bodies of Vertebrata is too strong to be 

 overlooked. Their assemblage constitutes a zone parallel to the 

 spht-rical surface of the capitulum, and lying at a slight distance 

 within it. Though it is impossible to assign to them, with cer- 

 tainty, their exact function, we feel compelled to regard the whole 

 system, including the bacillar tissue to which their stalks can be 

 traced (and which is only a locally modified portion of the nervous 

 zone, or zone of claviform tissue), as an apparatus of sense. It 

 would almost seem to represent a form of sense-organ, in which 

 sight and touch show themselves in one of their earliest phylogenetic 

 stages, in which they have not yet become fully differentiated from 

 one another. This is the only known instance of the existence in a 

 hydi'oid trophosome of any thing which may with fair reason be 

 regarded as a special a])paratus of sense. 



The male and female sporosacs are borne by the same tropho- 

 some. 



The generative elements, whether male or female, originate in a 

 special cavity (gonogenetic chamber), which is formed in the sub- 

 stance of the endoderm of the sporosac. 



In the female, the primitive plasma becomes gradually differen- 

 tiated into a multitude of cell-lilve bodies having all the characters 

 of true ova with their germiiial vesicle and spot. They are en- 

 tirely destitute of en'seloping membrane. 



These bodies next begin to coalesce with one another into 

 numerous roundish masses of protoplasm, a\ hich develop over their 

 surface minute pseudopodial retractile processes. 



The masses thus formed still further coalesce with one another ; 

 and there results a single spheroidal plasma-mass, through which 

 are dispersed numerous small spherical vesicles, mostly provided 

 A\ith a nucleus. These vesicles appear to be nothing more than the 

 nucleolated nuclei of the coalesced ovum-like cells. 



About the time of the completion of this last coalescence, the 

 resulting plasma-mass, enveloped in an external, very delicate, 

 structureless membrane, is expelled, by the contraction of the spo- 

 rosac, through an apertoure formed by rupture in its summit. 



