564 



DEVELOPMENT OF MEDUSAE. 



Fig. 304. DEVELOPMENT OF MEDUSJE. 



which are afterwards increased by the addition of many others 

 (g). In this manner a true polype is formed, which leads the 

 life of a Hydra, and, like it, propagates its kind by the forma- 

 tion of polype-buds, which detach themselves and lead inde- 

 pendent lives ; and thus from a single Medusan egg there may 

 arise a whole colony of polypes multiplied by gemmation. These 

 differ entirely from Hydras, however, in regard to their sexual 

 apparatus, which is detached (as in the" composite Hydrozoa) 

 under an entirely different form, that of a Medusa. The body of 



the polype undergoes a great 

 lengthening, and seems as if 

 divided by transverse bands, 

 which gradually deepen, so as 

 to make the whole body almost 

 resemble a pile of saucers 

 with divided edges (h) ; for 

 beneath the lowest of these 

 saucer-like disks, a new set 

 of polype -arms makes its 

 appearance ; and after the 

 detachment of the whole pile of disks, the polype-body 

 remains at their base, and may continue to lead its former 

 life, and to propagate itself in the polype-form. The disks 

 progressively enlarge, those at the summit of the pile in- 

 creasing most rapidly, and then detaching themselves from 

 the pile (i) ; when thus detached, they swim about freely in 

 the water after the manner of the smaller and simpler Me- 

 dusas, to which they closely correspond in form (d) ; and they 

 gradually enlarge and acquire the structure of their original 

 parents (&). It is not correct to represent (which is commonly 

 done) the pile of Medusa-disks as being formed 1 by the sub- 

 division of the polype-body. The Medusa-disks are in reality 

 sexual buds, resembling those of the composite Hydrozoa 

 ( 125); and the only essential difference between the two 

 cases lies in the fact, that among the latter it is the Zoophytic 

 form which ostensibly constitutes the animal (the Medusan 

 buds being thrown-off only at certain times for a special pur- 

 pose), whilst the former are only known (save to such as 

 search-out the history of their polypoid development) in the 

 Medusan stage of their lives. 



741. The recent researches of Professor Muller and others 



