CHAETODERMA HAWAIIENSIS. 51 



to others on the postabdomen .225 mm. long. Plate 37, fig. 12, gives an accurate 

 idea of the usual type of spine, these being from the middle of the metathorax. 



The mouth opening is situated about the centre of the frontal sense organ 

 and is remarkable for its minuteness. From here to the region of the radula 

 the canal is relatively small, not exceeding one seventh of the greatest diameter 

 of the prothorax. It is invested by a thin layer of muscles and is attached also 

 to a considerable number of scattered fibres that pass outward and are inserted 

 in the body wall. Ganglion cells arranged in groups as in the Neomeniidae are 

 also fastened to the buccal mass. The epithelial lining consists of high columnar 

 cells with basal nuclei imbedded in moderately dense cytoplasm, that more 

 distally becomes filled with a finely granular colorless secretion. In one speci- 

 men particles of a golden yellow color occurred in, or between, some of these 

 elements, but whether they were developed in situ, or had been produced by cells 

 more externally placed, it is impossible to determine. 



While in one specimen the digestive tract continues of about the same 

 calibre throughout, the other expands widely in the region of the radula, and at 

 the anterior end of this enlargement a circular fold is present that is probablj' 

 homologous with the proboscis of Drepanomenia, for example. In one indi- 

 vidual this swollen section is almost completely filled with diatoms, plant spores, 

 sponge spicules, and organic remains some of which appear to have been mixed 

 with some viscous secretion and moulded into globular masses. 



From a point corresponding to the hinder border of the globular part of the 

 prothorax to the anterior end of the preabdomen, the wall of the digestive tract 

 is relatively thin due to the scarcity of muscle fibres and the lowness of the epi- 

 thelial cells. The latter are columnar elements of medium height with spherical 

 basal nuclei and an abundance of a finely granular, light yellow substance filling 

 the entire distal half. At various points throughout the prothorax and meta- 

 thorax this substance is in the act of escaping in the form of droplets constricted 

 from the cell, and all stages exist between this and the development of a finely 

 granular secretion filling the canal. Cells freed of this secretion are cubical in 

 form and are usually relatively dense. Cleared specimens show that while in 

 this part of the gut true pouches do not exist the canal is by no means entirely 

 straight, wrinkles and folds occurring throughout, though they lack the definite- 

 ness and regularity of the dilations in the Neomeniidae. 



At the level of the front end of the gonad the development of digestive 

 fluids becomes relegated to a set of cells that form a large diverticulum extending 

 to the hind end of the body. In this digestive gland, judging from the material 



