202 CHAETODERMA BACILLUM. 



brick-red incrustation restricted to the spines surrounding the cloacal opening. 

 The two perfect individuals measure 11 nun. and 17 mm. respectively in length 

 by 0.9 mm. and 1.07 mm. in greatest diameter; the mutilated specimen was 

 approximately 13 mm. in length by 1.2 mm. greatest diameter. 



The spines are of the customary spearhead-type (Plate 11, fig. 4), with 

 moderate keels, and in the immediate neighborhood of the junction of the 

 pro- and metathorax range from 0.11 mm. to 0.16 mm. in length. In this 

 same region, at least, the hypodermal layer is clearly one cell thick, and gener- 

 ally speaking is composed of cells with clearly defined nuclei but invisible cell 

 boundaries (Plate 10, fig. 13). Among these are nuclei of the same general 

 appearance, but of twice the bulk, that are in contact with, and appear to 

 belong to, spherical or spheroid cavities containing in a preserved state a very 

 small quantity of a finely granular coagulum. What these spaces are it is 

 impossible to state definitely. They may contain calcareous salts in life or, 

 as in several other species, notably Chaetoderma attenuata, they may be gland 

 cells. At the base of each is a disc-Uke darkly staining body, presenting the 

 appearance of a nucleus though this is not conclusive. 



Delicate fibres traverse the underlying muscle layer at frequent intervals, 

 and come in contact with the hypodermal layer and at several points appear 

 to pass between the cells and then become lost to view. The nature of these 

 fibres has not been determined. They react somewhat as connective tissue 

 elsewhere in the body, and it may be mentioned are distributed to all of the 

 hypodermal elements alike. 



The buccal plate is partially exposed in one specimen only (Plate 11, fig. 6), 

 and appears to resemble a shield in form with the mouth holding a central 

 position. In sections the shield consists of the usual thick cuticular plate rest- 

 ing upon cells of several different types, judging by their form and arrangement. 

 Numerous muscle and large sized nerve fibres pass into the neighborhood of 

 the epithelial cells, but the absence of distinct cell boundaries renders it impos- 

 sible to determine their exact relations. Darkly staining masses, probably 

 cells though their details are aggravatingly difficult to determine, are attached 

 to the precerebral masses of ganglion cells, and from them dehcate ductules 

 make their way to the margins of the buccal plate. In some instances they 

 open through the cuticular plate; in other cases they pass to the outside of 



its borders. 



The mouth opens into a tubular canal without any particularly charac- 

 teristic features. The Uning epitheUum, consisting of columnar epitheUum 



