Reproduction in the Hydra viridis. 287 



layer of the animal's body ; then the cells of this layer seemed 

 to become thinner, and to recede from the outer covering or 

 capsule enveloping the egg-like mass, which had at the same 

 time become much thicker, and was now left attached to the 

 animal by a narrower portion or pedicle. In the further pro- 

 gress of development a similar solution or atrophy of the cells 

 of the pedicle was followed at last by the separation of the 

 spherical mass, which fell from the body of the polype to the 

 bottom of the vessel in which it was contained. 



The outer covering of this mass or capsule is described by 

 Ehrenberg as presenting in the Hydra aurantiaca^ on its outer 

 surface, a remarkable set of blunt prickles, many of which are 

 bifid at the end. In the Hydra viridis it forms a very strong, 

 elastic, and almost horny-like capsule, the surface of which is 

 rather tuberculated than spinous. The divisions between 

 the tubercles are irregularly hexagonal or pentagonal, and 

 their walls appear to contain a fibre, wound spirally round 

 them. 



In diflferent capsules, while still attached to the parent 

 animal, I observed the internal yolk or granular mass to 

 become subdivided into a number of smaller portions, each of 

 which was of a rounded form, and had a darker centre or 

 nucleus. From similar observations by V. Siebold, I am in- 

 clined to regard the fluid granular mass within the capsule as 

 the yolk of a single ovum, and the smaller masses into which 

 I have mentioned it became divided, as the result of that pe- 

 culiar process of cleavage of the substance of the yolk, and the 

 arrangement of the distinct portions round separate centres, 

 which was first discovered by Prevost and Dumas in Batra- 

 chia, and by Barry in Mammalia, and which is now known to 

 occur under certain modifications in the ova of all animals 

 previous to the formation of an embryonic membrane. I am, 

 therefore, disposed to consider the whole mass which is deve- 

 loped from the side of the polype in the manner before stated, 

 as constituting a single ovum, and as thus diflferent from the 

 multiple ovigerous capsules of the Coryne, and some other 

 allied polypes. 



I preserved several of the separated ova for some time, but 



