1905.] NATURAL SCIENCES OF PHILADELPHIA. 129 



nuclei of these cells are smaller and are easily distinguishable from the 

 retinular ganglion nuclei which lie near them (see text fig. 3). On 

 the edge of the nerve bundle this layer is continuous with the brain 

 sheath in the adult. The strands of protoplasm of which this layer of 

 cells is composed after it is perforated by the nerve fibres often run 

 up close to the basement membrane and might easily be mistaken for 

 nerve fibres to the outer pigment cells, but their origin indicates that 

 they are not nerves and there is no indication of any nervous connec- 

 tion for the pigment cells. 



Kenyon recognized this layer of cells, which he describes as follows i 1 

 "The outer mass (first fibrillar mass) presents a lunar appearance in 

 frontal sections (see fig. 1 of this paper), and lies close inside the base- 

 ment membrane of the retina, being separated from it by sufficient 

 space for the entrance of large tracheal sacs and a thin layer of cells 

 commingled with the fibres from the retina." It will be seen that 

 working with nerve methods this author did not recognize them as 

 nerve fibres, nor did he describe any nervous connection with the pig- 

 ment cells. Frequently these strands of protoplasm run close to the 

 basement membrane and there spread out as a pyramidal protoplasmic 

 mass lying between the nerve fibrils. This is particularly noticeable 

 in pupa stages before this layer of cells is so greatly distorted. 



The basement membrane is made up of a fusion of the proximal 

 ends of the outer pigment cells with the pigmented portion of the reti- 

 nular cells. This makes a sheet of cytoplasm, perforated where the 

 nerve fibres pass from the retinular cells, which can easily be macerated 

 away from the other elements of the eye and is easily distinguishable 

 on account of its deeply pigmented condition. The nerve fibres from 

 the retina pass through this and are seen as more or less separated on 

 a section through that region (fig. 18). This basement membrane is 

 continuous with the basement membrane of the hypodermal cells. 

 Fig. 10 shows diagrammatically the structure of the base of an^omma- 

 tidium and the elements which compose the basement membrane,' but 

 does not show the separation of nerve fibrils, since that is seen clearly 

 only in cross sections through that region. 



There are no trachese distal to the basement membrane in the com- 

 pound eye of the bee such as have been described in other eyes, espe- 

 cially among the Diptera. Exception must be taken to the statement 

 of Hickson 2 that "no spirally-marked trachese penetrate the optic tract 

 at any part of its course in Hymenoptera." Between the basement 



1 P. 369. 



2 P. 223. 



