56 CHAETODERMA ATTENUATA. 



merely to their form as the spicule mother cells do not contain any clearly de- 

 fined granular secretion. On the other hand the matrix cells shade much more 

 perfectly into the cubical elements that probably form the cuticle. 



The mouth, placed in a cleft on the dorsal side of the buccal plate, opens 

 into a tube whose form and general appearance are represented (Plate 25, fig. 1). 

 The lining epithelium consists of the usual high cohmmar cells produced into 

 several irregular longitudinal folds, through which the outlets of the buccal 

 glands make their way. These last named organs are comparatively abiuidaiit, 

 especially on the ventral side of the pharynx, and extend from the region of the 

 brain to the radula. 



A subradular organ certainly exists in this and several other species, if 

 position and innervation be any criterion. In material killed in vom Rath's 

 fluid it appears with the greatest distinctness as a sharply defined median area 

 composed of high columnar cells situated immediately in front of the peg-like 

 tooth (Plate 25, fig. 10). In alcoholic material the ajjpearance is not so striking, 

 and yet there is very little difficulty in distinguishing the organ. However, 

 with such material it is sometimes a task to determine its innervation. Nerves 

 in the immediate vicinity are usually visible, but to trace these into the ganglia 

 is frequently a perplexing o]ieration. In vom Rath's material on the other hand 

 the entire system is clearly differentiated (see section on nervous system). 



The radula and its supports (Plate 25, fig. 2) are of comparatively large size 

 but arc typically arranged and require nt) especial description. Beyond the 

 radula the gut becomes circular (Plate 25, fig. 3), the epithelium relatively high 

 and a iim^ly granular secretion fills the distal (wo thirds of the comjionent cells. 

 Among these are a very few more globular elements with a darkly staining more 

 granular secretion. Beyond the pharynx the gut widens, the cells become lower 

 and slightly glandular with the exception of a very few cells containing a yellow 

 secretion. Beyond this point the relations of stomach, intestine, and liver are 

 typical and require no detailed description. 



The brain and anterior portion of the nervous system closely resemble 

 what is found in C. erudita, and so require but little additional description. It 

 appears that the labio-buccal connectives have an origin independent of the 

 lateral and pedal, which as in C. erudita unite before entering the brain. The 

 commissures of the pedal cords are relatively more slender than those of C. 

 erudita, save the anterior one which is of exceptional thickness. In some cases 

 nerves arise from the commissures and are distributed to the body wall. 



The labio-buccal system is of unusual interest since it possesses what may 



