STRUCTURE AND DEVELOPMENT OF LEPIDOSTEUS. 829 



in the posterior half the walls are thick, and the mucous mem- 

 brane is raised into numerous longitudinal ridges. The peculiar 

 glandular structure of the epithelium of this part in the embryo 

 is shewn in Plate 40, fig. 62 (st.}. Its opening into the duo- 

 denum is provided with a very distinct pyloric valve (Py}. 

 This valve projects into a kind of chamber, freely communi- 

 cating with the duodenum, and containing four large pits (c'}, 

 into each of which a group of pyloric caeca opens. These caeca 

 form a fairly compact gland (c.) about 6-5 centims. long, which 

 overlaps the stomach anteriorly, and the duodenum posteriorly. 



Close to the pyloric valve, on its right side, is a small papilla, 

 on the apex of which the bile duct opens (b.d'}. 



A small, apparently glandular, mass closely connected with 

 the bile duct, in the position in which we have seen the pancreas 

 in the larva (Plate 40, figs. 62 and 63, /.), is almost certainly a 

 rudimentary pancreas, like that of many Teleostei ; but its 

 preservation was too bad for histological examination. We be- 

 lieve that the pancreas of Lepidosteus has hitherto been over- 

 looked. 



The small intestine passes straight backwards for about 

 8 centims., and then presents three compact coils. From the 

 end of these a section, about 5 centims. long, the walls of which 

 are much thicker, runs forwards. The intestine then again turns 

 backwards, making one spiral coil. -This spiral part passes 

 directly, without any sharp line of demarcation, into a short and 

 straight tube, which tapers slightly from before backwards, and 

 ends at the anus. The mucous membrane of the intestine for 

 about the first 3^5 centims. is smooth, and the muscular walls 

 thin : the rest of the small intestine has thick walls, and the 

 mucous membrane is reticulated. 



A short spiral valve (sp. v.}, with a very rudimentary epithelial 

 fold, making nearly two turns, begins in about the posterior half 

 of the spiral coil of the intestine, extending backwards for 

 slightly less than half the straight terminal portion of the in- 

 testine, and ending 4 centims. in front of the anus. Its total 

 length in one example was about 4'5 centims. 



The termination of the spiral valve is marked by a slight 

 constriction, and we may call the straight portion of the in- 

 testine behind it the rectum (re.}. 



