41 8 ELIZABETH KINNEV. 



the proximal region of some of these cells (follicle cells) there 

 has been seen a nebulous structure composed of very finely 

 divided black particles, which might be considered to indicate 

 an excessive deposition of fat in the tissue. This fine emulsion 

 might conceivably be coarsened at the boundary of the cell and 

 coalesce into fatty globules." 



In silk gland cells of A. americana and D. virginica which 

 were fixed with DaFano's modification of the Cajal method, 

 the same condition was found, but in these cases, there is a 

 greater tendency toward an arrangement of the granules in 

 rows, thus presenting the appearance of striations extending 

 from the lumen toward the periphery, and likewise a greater 

 grouping of granules around the edge of the cell toward the 

 lumen. These bodies tend to concentrate along all sections of 

 tracheae, thus outlining the course of tracheids very definitely. 

 In these two species, it must be remembered, active secretion of 

 silk only visibly appears at the time of forming the cocoon. 



It seems possible that these fine spherical granules may 

 represent by products of cellular activity that are being elimi- 

 nated. Their condensation along the tracheids and the proximal 

 border of the cell may indicate that such may be the case. In 



the two species in which the process of secretion is only in the 

 preparatory stage, an accumulation of waste products may be 



imagined to be occurring in the cell. 



3. The Membranes. 



(a) Historical. Before the work of Helm ('76), the existence 

 of a tunica propria, or external membrane, and a tunica intima, 

 or internal membrane was known and had been described, but 

 little was known concerning their structure or function. The 

 tunica propria was quickly dismissed by Helm and those following 

 him as a structureless membrane fitting very closely to the 

 l-a-al membrane throughout the entire extent of the gland that 

 roists to a considerable degree the penetration of fixing fluids. 

 But the tunica intima could not be so easily defined. Helm 

 describes its structure in the anterior region as containing fine 

 radial tubes which he refers to as "Porencanale." The entire 

 intima, according to his observations, represents a cuticular 



