264 NEW YORK STATE MUSEUM 



shell can now be removed and the animal immediately dissected, 

 or it can be placed in alcohol for future use. The alcohol must 

 be at first very weak, gradually increasing its strength each day. 



The advantage of a gelatin injection over a fluid one is that, 

 as the gelatin becomes hardened, dissections can be made with- 

 out danger of the escape of the injection from the severed blood 

 vessels. As the injection is a brilliant carmine, the blood vessels 

 stand out in bold relief from the light background of the various 

 organs. 



Heart. The heart (pi. 9, ], pi. 10, fig. 1, pi. 14, fig. 1, 30, 

 32) is situated in the outer portion of the first volution, just ante- 

 rior to the peristome, and is plainly visible from the exterior. Its 

 pulsations can be observed even through the shell. Ordinarily the 

 pulsations number about 45 or 50 a minute, in an adult indi- 

 vidual ; but are variable, sometimes being much faster, and during 

 hibernation slower. In a young individual the pulsations seem to 

 be much faster, sometimes equaling 150 a minute. The heart con- 

 sists of a single auricle and ventricle, inclosed in an oval pericar- 

 diac sac. The ventricle and auricle are pyriform, placed base to 

 base, the bases being somewhat truncated. The ventricle is about 

 twice the size of the auricle. 



In composition the walls consist of unstriped muscular fibers, 

 granulated, showing oval nuclei on the application of acetic acid. 



The interior of the heart is lined with tesselated epithelium, 

 consisting of granulated cells. The interior of the walls of the 

 aorta have a similar structure. 



The wall of the pericardium is very thin and transparent. The 

 pericardial fluid is very abundant, and, according to Dr 

 Leidy, is sometimes inhabited by an entozoon, named by him 

 Distoma vaga ns.^ Between the auricle and ventricle is a 

 valve, so disposed as to permit the passage of the blood only from 

 the auricle to the ventricle. 



Arteries (pi. 9, flg. 1). The ajK'x of thi' ventricle givt's origin 

 to one large aorta, which almost immediately subdivides, one 

 branch proceeding posteriorly, and supplying the digestive gland, 



ijonr. acad. nat. sci. new series, v. i Philadelphia. 



