THE DOGFISH 5 



In the forward part of the abdominal chamber is the large yel- 

 lowish or greenish liver ; it is composed of two principal lobes, 

 which meet in front and are attached to the false diaphragm by 

 a mesentery. Beneath and between the lobes of the liver lie the 

 stomach and the intestine. The latter is a large tube which pro- 

 ceeds directly back to the cloaca. The former is a bent V-shaped 

 tube in the forward and middle portions of the abdominal chamber, 

 extending forward beneath (dorsal to) the liver to the anterior 

 end of the cavity. In the spiny dogfish it consists of two distinct 

 portions,— a thick, straight, anterior portion and a V-shaped por- 

 tion,— which are separated from each other by a prominent con- 

 striction. Note the membranous mesentery which unites the two 

 limbs of the stomach. Attached to the bend of the stomach by a 

 mesentery, and extending back of it, is the large, dark-colored 

 spleen. At the point where the intestine leaves the stomach will be 

 seen a portion of the whitish pancreas. Note the gall bladder, em- 

 bedded in the liver. 



By pushing aside these organs, but not cutting them, the genital 

 organs will be seen lying against the dorsal wall of the body cavity. 

 If the animal is not yet adult, the genital glands (the testes or the 

 ovaries) will appear as a pair of elongated bodies of greater or less 

 size, but usually an inch or two in length, extending back from the 

 forward end of the abdominal cavity. The dogfishes which are 

 bought for dissection are often immature and contain only the 

 rudiments of the reproductive organs. 



If the animal is an adult male (and the sex may be determined 

 by the presence or absence of the claspers), the testes will appear 

 as a pair of elongated, flattened bodies, supported by mesenteries. 

 If the animal is an adult female, the ovaries will be seen,— ir- 

 regular, elongated bodies, usually with yellow spherical ova pro- 

 jecting from the surface. The oviducts are a pair of large tubes 

 lying against the dorsal wall of the abdominal cavity, at the for- 

 ward end of which their anterior ends fuse ; a single median open- 

 ing is present here on the ventral side of the fused ends, through 

 which the ova find their way into the oviducts from the abdominal 

 cavity. The extreme posterior end of each oviduct opens into the 

 cloaca by a pore at the side of the urinary papilla. 



