CHAETODERMA LUCIDUM. 199 



had dried prior to coming into my possession and are useless for the study of 

 the internal anatomy. The smaller specimens from both stations agree in 

 being relatively slender, and the larger specimens may retain this character- 

 istic or become relatively thick-set (Plate 9, fig. 12). 



The longest specimen measures 25 mm. in length by 0.75 mm. in greatest 

 diameter, while the individual with the greatest diameter, 1.2 mm., is 11.25 

 mm. long. The color of the specimens from the two stations is strikingly differ- 

 ent, though I am of the opinion that this is due to methods of preservation and 

 not to habitat. What appears to be the normal shade in a preserved state is 

 a gUstening Ught yellowish white somewhat darkened by the slaty gray liver 

 shining through the translucent body walls. A reddish yellow or reddish brown 

 incrustation, usually shading into dark brown in the larger individuals, gathers 

 on the spines about the cloacal opening. 



Bordering on the union of the pro- and metathorax the spines are in the 

 form of very thin flattened scales without any well-defined keel (Plate 9, fig. 15). 

 In length they range from 0.094 to 0.13 mm., while the width, even in spines 

 of the same length, varies as much as 30 per cent. 



The hypodermal layer presents no pecuUarities whatever save that the 

 giant cells of Wiren are more abundant than is usual in the region of the pro- 

 and metathorax where the hypodermis shows to the best advantage. In these 

 cells the nucleus is usually basally placed while the cell body contains little 

 save a finely granular coagulum adhering to the cell wall. As the spines in 

 this species have no clearly defined matrix cells in this species the possibility 

 presents itself that these larger hypodermal elements may play a part, but 

 there is nothing to prove conclusively that such is the case. On the other 

 hand they may correspond to the gland cells occurring in Chaetoderma aitenuata, 

 but the absence of attached fibres penetrating the somatic muscles renders 

 the identification uncertain. The remaining hypodermal elements are generally 

 cubical in form though the cell boundaries, unlike the sharply defined spheri- 

 cal nuclei, are very indistinct. 



The buccal plate is broadly shield-shaped with the mouth occupying a 

 deep cleft in the upper two thirds (Plate 10, fig. 11). In sections it is bounded 

 as usual by a heavy cuticular plate (Plate 10, fig. 2) resting upon a modified 

 hypodermal layer in which the cells appear with marked clearness though 

 without any especial pecuUarities. In a number of different species of this 

 genus there is a muscle bundle, probably acting as a sphincter oris and appear- 

 ing clearly in cross sections, and in the present species it is situated immedi- 

 ately internal to a well-defined sensory area that hkewise encircles the mouth. 



