88 ZOOPHYTES. 



above, fell over in a flattened form, as if incapable of sustaining itself up- 

 right. It would remain thus during two or three days at a time. 



According as the food is absorbed in the system, or as its residue is 

 rejected by the mouth, the symmetry of these animals is restored. 



It is not surprising that distension from inordinate voracity should 

 strain the narrow point of adhesion by so small a surface, and separation 

 ensue. But the effects of repletion are different on the hydra and actinia, 

 though, in many respects, they be much akin. The tentacula of the acti- 

 nia are then finely displayed, as if having enjoyed its repast ; while those 

 of the hydra remain closely contracted, fig. 16, and the body is distorted 

 as if suffering from immoderate indulgence. 



Though the natural colour of the Hydra tuba seems dingy white, 

 and always resolves into it, and though sometimes of orange or reddish 

 tinge when recovered from the sea, the quality of the food affects the hue, 

 and this for a considerable time. For example, specimens having fed on 

 the Gordim maximus, a large black or purple worm, continued darkly 

 stained for even two months afterwards. 



Both the aspect and the fertility of the animal depend on its treat- 

 ment. Nevertheless, many irregularities occur which cannot be traced to 

 definite sources. The number of external organs is frequently very variable 

 in some of the lower animals, and in none more so than the genus hydra, 

 where the character of all they have is similar. The finest adults of the 

 subject before us have at least 30 tentacula ; but one of the largest size 

 had only 16, while a young one, its progeny, still adhering to the body, 

 was perfectly mature. The parent of a group of four had 20 ; the farthest 

 advanced 16 ; and each of the other two had 12. The specimen, Plate XX. 

 fig. 7, n, had just 16 in four months after representation there; nor could 

 I find that the number had increased in three months longer. However, 

 the original complement of tentacula, as will be seen of the originating 

 hydra from another form, is two or four, advancing to eight and upwards. 

 As copious sustenance promotes fertility, some of the most numerous 

 of the preceding colonies might have been doubled by unremitting care. 

 The mode of propagation which I have described does not, in my 



