168 bulletin: museum of comparative zoology. 



a sort of operculum (Figure 14, op.). The epidermal cells upon ■which 

 this rests, and by which of course it has been produced, are much elon- 

 gated, and their deep ends are attached to a ligament (Figure 14, lig.). 

 To this ligament are attached, in turn, other elongated epidermal cells, 

 the basal ends of which are attached to the integument of the " toothed 

 process." I have no evidence that either set of these epidermal cells is 

 contractile, but they are both peculiarly elongated, and if they are 

 contractile we have here a mechanism for opening the external orifice 

 by depressing the operculum. This would allow the escape of the 

 excretory products, they being forced out by contractions of the 

 muscular layer of the wall of the vesicle. 



The space between the duct and the wall of the tubercle is filled by 

 the dermis (Figure 14, drm.), in which are found tegumental glands 

 {gl. e'drm.). At its base are striated muscles {mu.) belonging to the 

 antenna, but having no connection with the operculum. On the tubercle, 

 especially around the edge of its truncate face, there are numerous 

 sensory hairs (set. sns.). 



II. Development. 



A. Historical Summary. 



The published work on the development of the antennal glands in 

 decapod Crustacea is meagre and lacks both detail and completeness. 

 In most cases, it is only a by-product of researches along some other 

 line, or part of a general consideration of the life history of some 

 species ; this may account for the contradictory statements on the 

 subject. 



Rathke ('29) in a work much in advance of his time describes (p. 51) 

 for tlie crayfish embryo, at the time when pigmentation of the optic 

 lobes is well begun, the formation of a slender narrow plate, whose great- 

 est diameter is directed from dorsal-posterior to ventral-anterior. This 

 plate presents a rounded outline dorsally and ventrally ; its posterior 

 edire is concave ; its anterior convex. The outer surface is in contact 

 with the integument, the inner with the yolk, from which it has its 

 origin " through deposit of plastic material." The duct to the exterior 

 was not made out. These " Speicheldriisen," while remaining in con- 

 nection witli the yolk, increase in size and become more spherical 

 (p. GO). Just before hatching, there may be seen in these organs small 

 round green spots, the occurrence of wliich may be assumed to indicate 

 the beginning of secretory activity. When the yolk disappears, they 



