LYMNJEIDJE OF NORTH AMERICA. 7 



a. THE DIGESTIVE TRACT. Plate I. 



The alimentary tract is similar in general form and structure to 

 the other Pulmonata, differing, however, in some details. The mouth 

 is placed at the anterior end of the buccal sac, into which it opens; 

 the buccal sac (1) is somewhat pear-shaped, or long-ovate, when 

 viewed dorsally; it is very stout, being composed of strong muscle 

 fibers, and contains the jaw and odontophore ; the posterior side bears 

 the two buccal or stomato-gastric ganglia ; the oesophagus leaves the buc- 

 cal sac at the dorsal part of the posterior end (2), passing between the 

 various ganglia composing the nervous ring, and proceeds to the crop 

 in almost a straight line. The buccal sac is bluish in color, and the 

 oesophagus is dark brown or black. Just posterior to the buccal sac 

 the two salivary glands are placed; they are bright yellow in color, 

 irregular or ramose in shape, and are connected with the buccal sac 

 by four ducts (11) which enter the latter near the oesophagus. 



The region of the stomach is peculiar and was first correctly noted 

 in American Lymnaeas by Dr. R. P. Whitfield (op. cit.) in Bulimnea 

 megasoma. The oesophagus first enters the pyriform or elongate oval 

 crop (4), the stomach follows, and at first lies between two very mus- 

 cular organs, the bilobed gizzard (3) and then widens into the pyloric 

 portion (6), which gradually tapers to the intestine. The crop and 

 stomach are yellowish in color, while the gizzard is almost black. The 

 latter organ is very large, about the size of a small pea in species the 

 size of reflcxa, stagnalis and palustris, and composed of two concavo- 

 convex portions, almost surrounding the stomach, as described above. 

 They are more or less elliptical in outline, and their extremities are con- 

 nected by a number of stout muscle fibers of a silvery luster, as recorded 

 by Dr. Whitfield (op. cit.). The interior is hard and wrinkled, and 

 much resembles the gizzard of a fowl. The gizzard is as hard as a 

 pea, but the crop and stomach are soft and fleshy. A number of giz- 

 zards were cut open ; in freshly killed specimens, which had been in 

 captivity several months, the gizzards were empty, while in alcoholic 

 specimens they contained particles of siliceous matter. The figure of 

 the digestive system of Bulimnea megasoma in Prof. Wetherby's ar- 

 ticle 1 shows this gizzard, although its correct relation to the crop and 

 stomach is not mentioned. The walls of the stomach, crop and gizzard 

 are made up of strong muscle fibers. 



The intestine (5) is very long, and is marked by but one pro- 

 nounced flexure ; it makes one complete turn after leaving the stomach, 

 then follows the course of the last whorl and a half, bends upon itself, 



. Cin. Soc. Nat. Hist., Vol. II, 1879, p. 95, fig. 1. 



