ACALEPH^. 179 



detached, and assaming signs of independent life * ; swimming freely, 

 and acquiring, with a slight growth, a certain radiated form : but the 

 acquisition of the form of the parent by these buds has not been wit- 

 nessed. Martens observed small portions of the body of the Cestum 

 veneris detached, which moved independently for some time.f 



The most common mode of generation in the completed forms of 

 Acaleph(B is by the development of ova impregnated by sperma- 

 tozoa. In certain ciliogrades, e. g. Eucharis multicornis, the ova are 

 developed in the common cavity of the body along one side of each 

 longitudinal rib or ridge, and the testes on the other side ; so that 

 there are eight rows of ova and eight of testes. An efferent canal 

 extends from each row towards the mouth. This androgynous con- 

 dition, with the distinct stomach and chylaqueous cavity, indicates the 

 affinity of the Beroidae with the Actiniae. The pulmogrades are highly 

 prolific, and propagate in the ordinary manner by impregnated ova ; 

 the germs of which are developed in one set of individuals, whilst the 

 spermatozoa are developed in organs peculiar to other individuals, the 

 Acalephae of this order being male and female. Gaede first pointed 

 out the ovaria, and descx"ibed and figured the ova in the medusa. J 

 Ehrenberg confirmed and added to Gaede's observations of the fe- 

 males ; but he thought the spermatozoa of the male medusje parasitic 

 cercari<e, the testes and ovaria having the same form and colour in 

 the younger medusae § : but they are different in structure, and the 

 males have never the marsupial sacs on the arms. 



In Geryonia and Thaumantias the generative sacs are situated in 

 some part of the canals traversing the disc ; in Aurelia they are formed 

 by pushing in the wall of the stomach; in Rhyzostoma and Cephea they 

 are attached to the under wall of the stomach ; in Cyancea the organs 

 of generation are situated, in both sexes, in four cavities ^fig. 71, e, e,) 

 which push in the walls of the stomach and open on the under-part 

 of the disc, near the mouth. The females of Cyancea aurita are 

 distinguished, at the advanced stage of the breeding season, by the 

 numerous small flask-shaped marsupial sacs which are attached to 

 the under surface of the oral tentacles. 



Male medusae do not differ, in respect of size, from the females. 

 Siebold || finds that, when the Cyoncea aurita is but I^ in. to \^ in. 

 long, the males may be distinguished by the sperm-sacs in the t£enii- 

 form testis, and the females by the germ-vesicle and spot in the 

 similarly shaped ovaria ; but the band-like genital organ is small, and 

 instead of folds, shows only risings and depressions. When the 



* CXIV. p. 42. -f CLIII. p. -494. tf. i. fig. 2—4. 



X CXXXIX. taf. i. fig. 1. § CXL. || LV. p. 6. 



N 2 



