Chap. III. 



HYDRACTINIA POLYCLINA. 



231 



Fig. 34. 



The retiform stolon of Hy- 

 dractinia polyclina. From na- 

 ture, by H. J. Clark. 



a outer wall in profile, at the edge 

 of the depressions (d). — b inner 

 wall hollowed by the chymiferous 

 canals. — 61 granules circulating 

 in b. — f cells of a in profile. — 

 d depressions in the outer wall, 

 which appear sometimes to be 

 pierced. 



The inner wall [Fig. 3, h) is very thick, and constitutes the greater ])nlk of 

 the body ; it has the same extent as the outer wall, and is 

 in more intimate connection with the active functions of the 

 whole colony, forming the immediate lining of the digestive 

 cavity {d), which receives the cli3'miferous fluid, in common 

 with the other hydroids. Its inner surface is lined with an 

 irregular layer of brownish-red, coarse granules, of the same 

 nature as those [Figs. 5% y, and 5% c, wood-cut 34, b^ ; PI. 

 XXVI. Fi(). 18, b^, Vol. IV.) seen in the ramifying canals and 

 the sterile hydroids. The same ma}' be said of the cells of 

 this layer as of those of Coryne mirabilis (p. 205). 



From the 15th of December, 1855, to the SOtli of April, 

 1856, the fertile hydroids on our coast were free from medusa?- 

 buds, but from July to September, 1854, they were budding 

 copiously. At Charleston, South Carolina, they Avere found 

 budding from December, 1851, to February, 1852. During the 



unproductive season, we have found the sterile hydroids just as fully developed as at 

 any other time. We have never known any instances in which the tentacles 

 appeared to be resorbing, or indefinite in outline, except when the colony was 

 attached to a shell which was cast ashore by the tide, or dragged about by the 

 Hermit-crabs. In tide-pools, among the rocks to which they are attached, they 

 flourish most luxuriantly, and do not exhibit any signs of unhealthiness. Each 

 medusa-bud arises singly, in the form of a hernia, from the walls of its parent, 

 either closely together, and nearly on the same level with each other [Fig. 2, A 

 B C, 4, 4", and 4''), or scattered along the length of the body {Figs. 1, A B C, 

 and 3). 



Excepting that they contain spermatic particles instead of eggs, the medu- 

 soids of the males do not differ from those of the females, but owe their dissimi- 

 larity simply to the fact that the fecundating mass, which fills them, is yellow, 

 and uniformly diffused, whilst the eggs of the females are grayish, and present the 

 appearance of several distinct masses. During this season the colony is much more 

 crowded, and seems more densely packed than at any other time. Near the margin 

 of the colony the reproductive hydroids are higher, and even equal the sterile 

 forms in stature. Compare Fig. 1, A B, with D. Some of these have no buds 

 on them {Fig. 1, E), but in other respects are not different from the gravid ones 

 (Compare Fig. 1, E with A, and Fig. 2, A B C), not even in the apparently exclusive 

 peculiarity which they possess, usually toward the outskirts of the colony, of fre- 

 quently bending upon themselves till the head touches the base. On the extreme 

 border of the colony they are not resti-ained in their contortions, and may be 



