4l8 HOPKhWS. [Vol. XI. 



ing part curves upon itself to the right, and extends back- 

 ward about two-thirds the length of the abdominal cavity, 

 where it changes its direction and ascends to a point a little 

 cephalad of the middle of the cavity ; here it again forms a 

 loop, and thence extends directly to the vent. From this de- 

 scription and the diagram (Fig. i) it will be seen that there 

 are three descending and two ascending parts to the enteron. 

 The oesophagus and stomach are almost wholly included by 

 the two first portions, and it is with these that this paper has 

 chiefly to do. At the pyloric end of the stomach, in an adult 

 sturgeon, the walls attain a thickness of from two to four centi- 

 meters. Immediately following this thickened part are the 

 pyloric caeca. These appear like a single organ, but from the 

 occurrence of three distinct openings leading into the mass, 

 as Ryder (56) says, it must be regarded as a '' system of pyloric 

 caeca three in number"; the tubes soon subdivide into a num- 

 ber of small branches analogous to a racemose gland. The 

 remainder of the enteron will be passed over by simply re- 

 marking that the walls appear somewhat thin, and that at the 

 terminal end of the intestine the spiral valve makes seven com- 

 plete turns, the last one extending nearly to the vent. The 

 peritoneal coat has a uniformly dark, almost black, appearance, 

 due to the deposition of pigment (Fig. 5). Within the perito- 

 neum is the thin longitudinal muscular coat; the great bulk of 

 the muscular tissue, however, is comprised within the circular 

 layer. Along the oesophagus this layer is very thick, and the 

 striated fibers are grouped into large fascicles. In the gastric 

 region the striated muscular fibers are superseded by the un- 

 striated fibers; the circular layer is thinner, and the fascicles 

 are smaller and more compact. No oblique muscular coat was 

 observed. 



The various regions of the enteron are not sharply differen- 

 tiated from each other. In a general way the subdivisions can 

 be recognized, but the boundary line between oesophagus and 

 stomach, for instance, cannot be determined by the gross ap- 

 pearance of this region. A part, at least, of that portion which 

 most observers have called oesophagus ought, it is believed, to 

 be regarded as really a part of the stomach. 



