THE DOGFISH 



357 



which probably represents that of the right side of the 

 frog. It hangs into the body cavity and varies in size and 

 appearance with age. The ova are in different stages 

 of ripeness, the ripest being very large and yolky. They 

 are shed into the body cavity and passed forwards by 

 contractions of the abdominal walls to the front of the 

 peritoneal space, where they 

 enter the internal opening 

 of the oviducts. The latter 

 are large, straight tubes, one 

 on each side of the body, 

 attached to the dorsal wall 

 of the ccelom. They start 

 from a common opening in 

 the falciform ligament, not 

 far behind which each has 

 a round swelling known as 

 the shell gland. At the 

 hinder end of the trunk they 

 enter the cloaca by a com- 

 mon opening just behind 

 the anus. The testes are 

 a pair of long organs slung 

 by membranes from the 

 dorsal wall of the ccelom. 

 Each communicates at its 

 front end with the meso- FlG - 256.— An embryo dogfish 



nephros Of its Side by several in *s egg-case (" mermaid's 



r ,, „ ' . , purse ) which has been cut 



small vasa efterentia, the open to show the contents.— 

 sperm passing through these From Thomson. 



into the meSOnephric tubules d./., Dorsal fin fold; e.g., "external" 

 nnrl rhpnr-p tn trip vps rip gills; rf., stalk of yolk-sac; T., ten- 



ana tnence to tne vas ae- drilSj pro i on g ations of egg -case by 



ferens Or Wolffian duct, by means of which it is moored to sea- 



, • 1 .. j weed ; y. s., yolk-sac. 



which it is conveyed to 



the urinogenital sinus. A rudiment of the internal open- 

 ing of the oviducts is found in the falciform ligament of 

 the male. Sperm is passed by the aid of the claspers 

 into the cloaca of the female and fertilisation takes place 

 within her. The eggs are laid in flat, oblong, brown shells 

 whose angles are prolonged into tapering tendrils, which 

 twine round seaweeds and thus anchor the egg. Protected 



