PLUMATELLA. 131 



After careful preservation during winter, the shells of the ova began 

 to sunder, and give birth to the young hydra of the Plumatella on the 

 10th of May. Numbers continued hatching for two weeks successively. 

 —Figs. 12, 13, 14, 15. 



On computing the period requisite for bringing the embryo to per- 

 fection, from October 22d until May 10th, it appears to extend to at least 

 198 days. 



But many ova having remained entire considerably later, the interval 

 must be rated longer in proportion. Thus, the period elapsing between 

 the delineation of the ova in fig. 10, and the young hydra hatched from 

 one of them, fig. 15, amounted to seven months. The whole hydra? re- 

 presented, figs. 12, 13, 14, 15, represent the young brood from other ova 

 of fig. 10, there being additional ova or shells in their vicinity. 



The horizontal position of the ova in the branches was still preserved 

 by those remaining there in June. None hatched after the 24th of that 

 month. 



Similar general principles, perhaps, predominate over the propagation 

 of other specimens, without perfect uniformity in the detail, which is 

 scarcely surprising, seeing that we cannot declare the identity of species. 

 There may be varieties, or a great difference may be concomitant on age, 

 and something may depend on season. 



A specimen investing a leaf of the Water Plantain, the hydra of which 

 had 60 tentacula, is above referred to (p. 126), Plate XXXII. figs. 1, 2. 

 The hydrse of that last quoted diffusing on the leaf of the Iris, had only 

 50 tentacula. — Fig. 8. 



Numerous ova occupied the tubular parts of the former on the Water 

 Plantain, in the middle of August ; and some had escaped on the 20th of 

 that month, of lenticular form like the others, with a smooth edge, dark 

 circumferential ring, and yellow disc or centre. — Fig. 4. 



But, besides the ova in the tubes, some were contained in the body 

 of the hydra?, between the integumentary skin and the interior organs, 

 wherein they rose high. One of the hydra? had at least six. Ova also 

 occupied the cavities of those tubular ramifications, which, at this time, 

 were vacant of hydra?. 



