CHAP, x DEVELOPMENT 469 



side only are drawn. Tn A the seminal vesicle and sperm-sac are dissected away 

 from the kidneys and displaced outwards, and the ureters inwards. 

 ab. p. depression into which the abdominal pore opens ; cl. cloaca ; els. clasper ; 

 ef. d. efferent ducts of spermary ; k. kidney ; k' (in B) vestigial portion of the 

 kidney ; k', k" (in A) epididymis ; Ir. anterior portion of liver ; m. d. vestigial 

 oviduct in the male ; oes. gullet ; ov. ovary ; ovd. oviduct containing egg ; 

 ovd' its ccelomic aperture ; ovd". the common aperture of the oviducts into the 

 cloaca ; r. rectum ; sh. gl. shell-gland ; spd. spermiduct ; sp. s. sperm sac ; s. v. 

 seminal vesicle ; s. v'. its aperture into the urinogenital sinus ; ts. spermary ; 

 u. g. s. urinogenital sinus ; ur. ureters ; ur'. their apertures into the urinogenital 

 sinus ; . s. urinary sinus. 



narrow and thin-walled ; the posterior two-thirds is wide 

 and distensible, and at the junction of the two parts is a 

 yellowish glandular region, the shell-gland (sh. gl). A 

 vestige of the anterior ends of the oviducts can be 

 recognised in the male (A, m. d). 



Development.^ Impregnation is internal, and is 

 effected through the agency of the claspers of the male 

 (p. 433). The eggs, when ripe, break loose from the 

 surface of the ovary into the coelome, and thence pass, 

 through the common oviducal aperture, into one or 

 other of the oviducts, where fertilisation occurs. On 

 reaching the dilated portion of the oviduct, the oosperm 

 of Scyllium becomes surrounded first by a gelatinous 

 substance, and then by a horny egg-shell or " Mermaid's 

 purse" 1 secreted by the shell-gland, and having the 

 form of a pillow-case produced at each of its four angles 

 into a long, tendril-like process. The eggs are laid among 

 sea-weed, to which they become attached by their 

 tendrils. In Acanthias and Mustelus (p. 431) a mere 

 vestige of the egg-shell is formed, and the eggs undergo 

 the whole of their development in the oviducts, the 

 young being eventually born alive with the form and 

 proportions of the adult. 



The great size of the egg is due to the immense 

 quantity of yolk it contains : its protoplasm is almost 

 entirely aggregated at one pole, where it forms a small 



1 An egg is contained in the oviduct shown in Fig. 127, B. 



