THE DEC APOD A 



281 



resembles that of many of the more primitive Malacostraca. A 

 deep transverse infolding of the dorsal surface, which marks the 

 division into the larger anterior or cardiac and the smaller posterior 

 pyloric chamber, is produced internally into a strong median tooth 

 (m.t). The floor of the cardiac chamber presents internally a median 

 (m.r) and a pair of lateral (l.r) longitudinal ridges defined by deep fold- 

 ings of the cuticle and representing elements which in other forms 

 become calcified sclerites ; just above these on each side are series 

 of stout denticles (d), of which a posterior group in the vicinity of the 

 "median tooth" appear to correspond to the " lateral teeth " of other 

 Decapods. The pyloric division has its lumen greatly reduced by 

 infold ings of its walls, and may be regarded as being divided by a 

 longitudinal fold (r) on each side into a dorsal and a ventral portion, 



card. 



[ 



FIG. 16G. 



Dissection of the stomach of Cemtaspis moiistruosus (semi-diagrammatic). cf'nJ, cardiac 

 chamber ; d, lateral denticles ; I, terminal lappets projecting into mid-gut ; l:r, lateral ridge ; 

 m.r, median ventral ridge of cardiac chamber; m.t, median tooth ; jnfl, pyloric chamber; r, 

 longitudinal ridge separating dorsal and ventral divisions of pyloric chamber ; .', wedge- 

 shaped ridge with straining apparatus. (After Bonnier.) 



of which the former is a direct continuation of the cardiac chamber, 

 while the latter is a diverticulum closed in front and communi- 

 cating with the dorsal chamber only by a narrow slit between the 

 setose margins of the longitudinal ridges. The ventral chamber 

 has its cavity again divided into two portions by a strong median 

 wedge-shaped ridge (w) which rises from its floor and is produced 

 posteriorly into a, tongue-like process overhanging the apertures of 

 the hepatic ducts into the mid-gut. The lateral surfaces of this 

 ridge are provided with a characteristic armature which seems to 

 act as a straining apparatus ; it consists of numerous parallel plate- 

 like ridges running longitudinally and standing at right angles to 

 the surface, each bearing on its edge a comb-like fringe of setae 

 lying parallel with the surface and covering in the groove lying 

 between each ridge and the next. This wedge-shaped ridge and 



