CHAETODERMA ATTENUATA. 55 



and leads to tlic irresistil)l(> ('nnflusioii that here the coelomoducts are not only 

 morphologically related to the n>nal organs in the Chitons or other molluscs, 

 but i)hysiologieally also as Wiren first clearly stated. 



Chaetoderma attenuata, sp. nov. 



Eight specimens of this species were dredged near the southern limit of 

 Alaska, buried in glacial mud brought down chiefly by the Stikine River. One 

 from Kasaan Bay (8ta. 4244) occurred in green mud at a depth of 50-54 fathoms; 

 five opposite the mouth of the Stikine River (Sta. 4250) were in the same habitat 

 at a depth of 61-66 faths. ; while two in the waters of Stephens Passage (Sta. 

 4252) were buried in gray mud at a depth of 198-201 faths. Their appearance 

 in life, Plate 4, fig. 3, answers closely for preserved material. The type specimen 

 measured 45 nun. in length by 1.7 mm. through the metathcrax, and 2.6 mm. 

 through the abdomen. The color of alcoholic material, which is the same as 

 the living save for the pinkish tinge due to haemaglobin in the head and gill 

 region, is almost white with a tinge of yellow, becoming grayish where the liver 

 is located. 



The body wall, including muscular, hypodermal, and cuticidar layers, is 

 of median thickness and is typically located, but in specimens killed in vom 

 Rath's fluid certain elements appear that have not been fully described, though 

 they probably occur in all species of the genus. These are the so-called giant 

 cells (Riesenzellen Wiren) which in ordinary material present the form of empty 

 vesicles with the nucleus mibeddetl in the wall. In life this cavity is tilled with 

 a secretion, that after treatment with fluids containing osmic acid, is granular as 

 Wiren has remarked. In favorable situations it may readily be seen that fibres, 

 muscular at least in part, e.xtend from the somatic musculature and penetrating 

 the hypodermal la.yer attach to the sides of these cells (Plate 25, fig. 7). Ap- 

 pearances suggest that the secretion, upon the contraction of the fibres, is forced 

 into the neighboring lacunae, but in no case has this been actually observed 

 though proximally the cell may be produced into a comparatively slender, short 

 stalk. Distally the cells are usually in close contact with the free surface of the 

 cuticle and present a sharply defined rounded appearance. Posteriorly these 

 elements become somewhat less numerous and of smaller size. In alcoholic 

 killed material the fibres may be distinguished, but their attachment to the cell 

 body is very indistinct. 



Wiren ('92) states that these giant cells are not sharply differentiated from 

 the basal matrix cells of the spicules, but this refers, so far as I am able to judge, 



