Reproduction in the Hydra viridis, 285 



•ber^ is, however, an exception, mentioning that he has seen the 

 ova formed in the month of June. A succession of ova are 

 observed to be formed on, and detached from, the same polype ; 

 and according to V. Siebold, the parent generally dies after 

 the separation of the last of the series. The development of 

 fecundated ova, therefore, at the approach of winter, may be 

 regarded as a means of security against the extinction of the 

 species through the death of the entire animals by cold or 

 want. The ova probably remain for a considerable time in 

 an undeveloped condition. 



The extreme simplicity of the organs in question is a feature 

 of some interest. In order to explain this, I may state that 

 the wall of the body of the hydra, though endowed with a 

 digestive and assimilative faculty, and possessed of sensitive 

 and motor powers to a remarkable degree, is yet composed of 

 no other structure than organised cells united together by 

 their adjacent parietes, so as to form two layers ; of which the 

 innermost contains the green granules, which give colour to 

 the most of the animal ; and the outer presents, studded over 

 its surface, those peculiar forms of cells from which the sting- 

 ing or poison filaments protrude, with which the animal, in 

 seizing its prey with its tentacula, appears at once to stupify 

 and to fasten them. No nervous or muscular fibre, no special 

 glandular organs, are visible; but every cell for itself, and the 

 whole mass of them- in concert, appear to be capable of the acts 

 of assimilation, and to execute their movements under the influ- 

 ence of sensations by a texture of a similar cellular organiza- 

 tion throughout. 



The development, therefore, from so simple a texture of 

 organs possessing so obvious and peculiar a form and structure 

 as the spermatic and ovigerous capsules, is a very striking 

 phenomenon. 



The conical eminences which constitute the spermatic cap- 

 sules appear to consist, in the greater degree of development, of 

 one or more of the superficial cells in the vicinity of the base 

 of the arms. These capsules sometimes occur in considerable 

 numbers, as from eight to sixteen on the brown polype; 



