300 



THE ELASMOBRANCH FISHES 



Tertiary Bowman's capsules result from the further fragmentation of the 

 remains of the inferior and superior parts of the median vesicle. These, like 

 the secondary capsules, are gourd-like and their termini unite with tertiary 

 processes. The tertiary collecting tubules {III, fig. 258e) result in part as 

 processes which spring from the sides of the origin of the secondary process. 

 These pass to meet and fuse with the tertiary Bowman's capsules. 



At this stage, Acanthias, 8 cm., each body segment has one primary (/) , two 

 secondary (//), and four tertiary Bowman's capsules (III). Four of these, 

 one primary, one secondary, and two tertiary, belong to the median vesicle 

 from which the primary was derived; the remainder arise from the following 



vesicle. By the time the adult stage is 

 reached luimerous renal corpuscles and 

 renal tul)ules are present in each seg- 

 ment. In fact it is these, together watli 

 connective tissue, which make up the 

 mass of the kidney. 



Genital System 



Fig. 259. Early sex cells, Acanthias. 

 (From Woods.) 

 p.o., primitive ova. 



The genital system consists of the sex 

 glands and their tubes. The adult glands 

 arise as a collection of germ cells {p.o., fig. 259) , which, before passing into the 

 glands are scattered more or less widely in the tissues. These cells appear very 

 early and are well shown before a genital ridge is formed. They later, through 

 migration, take up their position in the sex gland. At this early "indifferent" 

 stage it is impossible to tell what the sex of the individual will be. The cells 

 then begin to specialize and to take on the characters of the sex cell of the male 

 or the female, whereupon the glands become the testes or the ovaries, respec- 

 tively. We shall describe these organs in the male first. 



GENITAL ORGANS OF MALE 

 TESTES 



The paired testes of the male vary considerably in size. In some of the Elasmo- 

 branchs they are relatively small {Torpedo) ; while in many others, especially 

 during the breeding season, they are of large size (Heterodontus; Raja clavata, 

 fig. 254b) . It often happens at this time that the testes are irregular in outline, 

 being made up of numerous lobes {t., fig. 253b, Squalus siichlii). In certain 

 forms the testes may be connected posteriorly with the rectal gland by a heavy 

 mass of tissue, the epigonal organ {Heterodontus, Scyllium), a vestige of 

 which we saw in Heptanchus. An epigonal organ, however, is only slightly 

 developed or entirely wanting in many types {Acanthias, fig. 253; Squatina, 

 fig. 254a ; and Torpedo). 



