LYMNiEIMi OF NORTH AMERICA. 17 



only in the general shape of width and length. The ureter in some 

 species (as stagnalis 1 ) 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- Kef erstein, 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 oesophagus 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 {ccphalica 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 Lymnseas, especially stagiialis, 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. 2 The fluid has been 

 called hcemocyanin by Williams. 3 It is colorless when unoxidized, but 

 becomes bluish when oxidized by the air. The haemolymph 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 frotractors of the sexual organs. The tentacle*, 

 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. 

 (PI. IV, fig. F. 2; pi. I, fig. 52.) Several small muscles protract and 

 depress the buccal body. (PI. IV, fig. F, 5.) 



^ee Pilsbry, Proc. Phil. Acad., 1900, plate XVII, fig. 2, for a figure of the 

 kidney of stagnalis. 



2 See Nelson, Quart. Jour. Conch. 1877, no. 11, p. 216. 

 3 Journ. Conch., VI, p. 122, 1889. 



