LYMNEID/ OF NORTH AMERICA. nity 
only in the general shape of width and length. The ureter in some 
species (as stagnalis’) is a trifle longer than in others (as reflexa). 
h. THE CIRCULATORY SYSTEM. 
The circulatory system does not differ materially from that of 
the pulmonates in general, being similar to the descriptions and figures 
published ‘by Keferstein, Leidy and Simpson. 
The heart is on the left side of the animal, at the apex of the 
respiratory cavity, and lies laterally between the cesophagus and the 
rectum, and not far from the stomach. The ventricle and auricle lie 
in a large oblong pericardium (34, 35, 36). The large aorta divides 
into the two branches (cephalica and visceralis) as in the other Pul- 
monata. The respiratory, circulatory and renal systems are closely 
related, both in structure and function. 
Some of the Lymnzas, especially stagnalis, have been seen to 
discharge a quantity of a pale violet colored fluid when irritated; 
this color is so intense in some specimens as to tinge the water with 
violet when the animal is placed in scalding water.? The fluid has been 
called hemocyanin by Williams.* It is colorless when unoxidized, but 
becomes bluish when oxidized by the air. The hemolymph of the 
animal contains this fluid, which is a respiratory substance consisting 
of copper united with a proteid. It is probable that some sudden shock 
causes the rupture of the veins containing the fluid. It has also been 
observed in a number of the American stagnalis appressa. 
i. THE MUSCULAR SYSTEM. Plates I and IV. 
Besides the columella muscle and the muscular tissue forming the 
walls of the different organs, there are a number of free muscles of 
great importance. These are the RETRACTORS of the buccal body, and 
the RETRACTORS and PROTRACTORS of the sexual organs. The tentacles, 
not being retractile, have no free muscles of importance. 
The buccal sac is retracted by two long muscles which are attached 
distally to the columella muscle at some distance from each other. In 
the Pulmonata Stylommatophora the two branches of the buccal re- 
tractors unite to form one muscular band before being inserted in the 
columella muscle, thus differing radically from the Basommatophora. 
(Pl. IV, fig. F. 2; pl. I, fig. 52.) Several small muscles protract and 
depress the buccal body. (PI. IV, fig. F, 5.) 
1See Pilsbry, Proc. Phil. Acad., 1900, plate XVII, fig. 2, for a figure of the 
kidney of stagnalis. 
2See Nelson, Quart. eS. Conch, 1877, no. 11, p. 216. 
sJourn, Conch., WE, p. 222) 1889. 
