WAITE: ANTENNAL GLANDS IN HOMARUS AMEEIGANUS. 187 



the adult gland, but iu this larval stage there are no globular promi- 

 nences extending out from it into the lumen. 



The histological structure of the duct is shown in Figure 60 (Plate 6), 

 which is from a longitudinal section of the appendage. Its wall is di- 

 rectly continuous with the body wall. The dorsal lip of the orifice {of. 

 ex.) shows no abrupt transition from the wall of the duct to that of the 

 body. On the ventral lip the limit is somewhat more precise owing to 

 the sharp folding, but it is difficult to say to which wall the apical cells 

 of the ventral lip belong. The cells of the dorsal wall show differences 

 in size and shape among themselves, and a considerable difference from 

 the cells of the ventral wall ; these being smaller and imbricated. The 

 cells of the duct do not show the granular striatum characteristic of the 

 cells of the ectodermic sac, nor is there a striate cuticula on the face 

 of these cells. These two characters serve to distinguish the cells of 

 the duct from those of the ectodermic sac. and lead to the inference that 

 the former have no secretory function. However, as one follows the 

 wall of the ectodermic sac as it merges into the wall of the duct, these 

 two characters gradually disappear, and it is impossible to say that there 

 is any definite line where ectodermic sac ends and duct begins, — a con- 

 dition to be expected from the fact of their having had a common origin. 



The cuticular layer of the external shell bends into the duct (Fig. 60), 

 but soon thins out and disappears. It extends for a greater distance 

 along the dorsal than along the ventral wall. 



The lumen of the ectodermic sac contains a granular coagulum, which 

 resembles in staining properties that seen in various parts of the adult 

 gland, but there is no trace of the globular structures there seen (p. 166). 

 This coagulum is in all probability the secretion of the walls of the ecto- 

 dermic sac, indicating that the functional activity of the gland has 

 already begun ; but that function must differ in some respects from the 

 function in the adult, as indicated by the absence of the globules. This 

 coagulum is not seen in the lumen of the endsac. The identity of the 

 substance found here with that found in the adult gland can only be 

 established by micro-chemical tests, and for that my material is not 

 suited. 



It seems probable that the function, although possibly somewhat 

 different from that of the adult, is of essentially the same nature, i. e. 

 excretory. This would be expected both upon a priori grounds and 

 from the structure of the cells as described. At this stage metabolism, 

 consequent upon the activity of the larva, is constant, and as all the 

 structural conditions appear favorable, it seems as if this organ, which 



