Chilton. — On Astacus fluviatilis and Paranephrops setosus. 161 



ossicles {'p G ) have much the same shape and position as in Astacus. The 

 lateral teeth (It) are large and reddish-yellow in colour. Anteriorly the 

 teeth are large and distinct and there is one large tooth placed on one side 

 of the row ; posteriorly the teeth decrease greatly in size, but there are two 

 or three rows so that they form an efficient grinding apparatus. Beneath 

 the lateral teeth on each side there is a small, single, sharp tooth at the 

 end of a long, thin, calcified bar. In a side view of the stomach (fig. 6) this 

 tooth is seen to be also supported by a broad plate, the inner surface of 

 which is thickly covered with short, stiff, plumose setse. On the raised 

 edge of this plate, projecting from either side into the interior of the 

 stomach, there is a row of setas similar to the others except in length. 

 These stretch across and meet in the centre and appear to be for the 

 purpose of stopping the food and forcing it to pass through the gastric 

 armature already described. They (pi. XXI., fig. 6) are very long and 

 slender, of the same size throughout almost the whole of their length, 

 often slightly curved towards the end. The stem is unjointed and is 

 covered with filaments, which are not much longer than the diameter of 

 the stem itself. 



The pyloric portion of the stomach seems to be essentially the same as 

 in Astacus. The ccecum (pi. XX., fig. 6 cce) appears to be variable, for 

 though I have seen it quite distinctly in some specimens, I have been 

 unable after careful search to find it in others. The cardio-pyloric valve 

 (cpv) is present as in Astacus, and the transverse section of the pyloric 

 region is so very much like that of Astacus that I have not given a figure of 

 it.* At the opening of the pyloric sac into the intestine there are valves, 

 one median, one above, and apparently only one on each side. 



From the pyloric end of the stomach the intestine passes direct to the 

 anus on the ventral surface of the telson. There is no coecum in connection 

 with the rectum as there is in the lobster, Homarus vulgaris.] 



At the sides of the stomach gastroliths were found in some specimens. 

 These evidently differ much in shape according to their state of develop- 

 ment, and when fully developed they differ considerably from those of 

 Astacus. The side turned towards the stomach is either flat or slightly 

 concave. The part which forms the convex side is doubled over so as to 

 join with the flat or concave side, the junction between the two forms a well- 

 marked nearly circular indentation. The flat or concave portion inside this 

 ring is quite smooth. The convex side is more convex than the correspond- 

 ing part in the gastroliths of Astacus, and it also differs in being quite 



* See " The Crayfish," p. 53, fig. 9 E. 



t See Huxley and Martin's " Practical Biology," p. 133. 



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