108 LECTURE IX. 



manner of animals from impregnated ova, the germs of which are 

 developed in organs or ovaria peculiar to one set of individuals, while 

 the fertilising filaments are prepared by testes peculiar to other indi- 

 viduals ; the Acalephse being male and female or dicecious. TJie 

 generative organs in Rhizostoma, CyantEa, and many other Medusae, 

 are situated in both sexes in four cavities {fig- 53. e, e), which open 

 on the under part of the disc, near the mouth. The testes and 

 ovaria have the same form and colour, but are different in structure. 

 The females of Cyancea aurita are distinguished by having numerous 

 small flask-shaped sacs developed from the under surface of the oral 

 peduncles or arms. The sexes do not differ in size. 



Each testis consists of a plicated band of membrane, bent in the 

 form of a bow, with the convexity attached to the concave wall 

 which divides the generative cavity from the stomach. If a probe 

 be inserted in the generative cavity, it immediately touches the 

 under surface of the testis ; if it be inserted in the digestive cavity, 

 it touches the upper surface of the testis, but not immediately, be- 

 cause the epithelium of the digestive cavity covers that surface. 

 The testis is much longer than the cavity containing it, but is adapted 

 thereto by its numerous convolutions. Its concave side gives off a 

 numerous series of highly irritable coloured tentacles, having the 

 same structure as those on the arms. They are richly ciliated, 

 and contain many peculiar hyaline rounded corpuscules immediately 

 beneath the surface. The spermatic tentacles are capable of only 

 moderate extension, and, at the breeding season, they project from 

 the mouth of the generative cavity, leaving only a small passage at 

 their centre. By their powerful ciliary apparatus they keep up a 

 strong current of sea water, and thus aid in the expulsion of the 

 semen. 



The parenchyma of the testis consists of a transparent granular 

 substance, in which are imbedded innumerable pyriform sacs, having 

 their bases turned towards the upper surface of the testis, and their 

 apical orifices opening upon their under surface, which they render 

 uneven by their tumid margins. The spermatozoa are developed in 

 these sacculi, which permanently represent the earliest rudiments of 

 the extremely elongated seminal tubes in the higher animals. The 

 parietes of the seminal sacs are pretty thick, and perhaps contractile. 

 A terminal enlargement, or body, and a ciliated appendage may be 

 distinguished in the spermatozoa : the latter part manifests an undu- 

 latory movement. The fasciculus of spermatozoa does not exhibit 

 these parts, in the same degree of development, in each sperm sac. 

 Those nearest the cervix of the sac are the most perfect. The ciliary 

 appendages of the spermatozoa are always directed towards the 

 opening of the sperm-sac. The bundles of these filaments follow each 



