80 Rev. T. Hincks on the Reproduction of Clavatella. 



M. de Quatrefages records the occurrence of ova in Eleutheria, 

 in the same portion of the body which they occupied in the zooid 

 of Clavatella. He says they are developed " entre les tegumens 

 et la par tie inferieure du corps, au milieu de la gangue trans- 

 par ente" They would seem to be a product of the ectoderm. 

 He observed them in the state of segmentation (" composes d'une 

 petite agglomeration irreguliere de granules "), and describes them 

 as assuming at a later stage a spherical form, and being sur- 

 rounded by a very distinct transparent membrane. As the eggs 

 increased, they pushed out the integument, which at length 

 formed a pouch, the size of which equalled that of the animal 

 itself. It contained a " transparent granular substance" (Pl.VIII. 

 fig. 4 a). In the case of the Clavatella, the proximal portion of 

 the zooid became much distended as the development of the ova 

 proceeded, and presented at last a very gibbous appearance. 



The young of the Clavatella is no doubt a ciliated embryo, 

 similar to that of other Hydrozoa; but I have never seen it 

 actually liberated. In an early stage of development the polype 

 consists of a short clavate body, with only two tentacles, placed 

 at opposite sides of the head (PI. VIII. fig. i). The number of 

 arms increases with the age of the polype. I have met with 

 four, five, six, and seven, but never more. Occasionally one 

 occurs of smaller size than the rest, and evidently of later 

 growth. 



I have not succeeded in clearly distinguishing the male zooid ; 

 but on one occasion an individual, which had passed into the 

 quiescent state, was seen surrounded by a multitude of minute, 

 actively-moving bodies, which I fancied might be spermatozoa. 



The genus Clavatella presents us with a striking group of 

 distinctive characters. Of these the most remarkable undoubt- 

 edly is to be found in the structure of the sexual organs. The 

 history of its reproduction, indeed, supplies us with a new class 

 of facts. 



The production of free sexual zooids for the propagation and 

 diffusion of the species is of common occurrence among the 

 Hydrozoa; but, so far as hitherto observed, these motive buds 

 always assume a Medusan organization — consisting, that is, of 

 a polypoid body, more or less developed, invested by a contrac- 

 tile calyx, which serves as an organ of propulsion. The genera- 

 tive elements are elaborated either in the walls of the central sac 

 or of the canals which traverse the swimming-bell. But in the 

 case of Clavatella, there is no trace of Medusan structure in the 

 reproductive bud. The free zooid is no longer a swimmer, but 

 a crawler and climber. A new locomotive apparatus is intro- 

 duced, which is Echinodermal rather than Hydrozoan. The 

 simple polype structure is very slightly modified in the repro- 



