On the Structure and Development of Myriothela. 299 
appears to be but a modification of the tissue which elsewhere 
forms the zone of claviform tissue. 
Extending in a radiating 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. Within this sac, and completely 
filling it, is an oviform capsule with firm transparent walls, and 
haying 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. Notwithstanding 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 
spherical 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 
hydroid trophosome of any thing which may with fair reason be 
regarded as a special apparatus 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-like bodies having all the characters 
of true ova with their germinal vesicle and spot. They are en- 
tirely destitute of enveloping membrane. 
These bodies next begin to coalesce with one another into 
numerous roundish masses of protoplasm, which develop over their 
surface minute pseudopodial retractile processes. 
The masses thus formed still further coalesce with one another ; 
and there results a smgle spheroidal plasma-mass, through which 
are dispersed numerous small spherical vesicles, mostly provided 
with anucleus. These vesicles appear to be nothing more than the 
nucleolated nuclei of the coalesced ovum-lke 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 aperture formed by rupture in its summit. 
