1905.] NATURAL SCIENCES OF PHILADELPHIA. 145 



distal to the retinular spindle. The nuclei are large and spherical, 

 and lie slightly distal to the centre of the cell. The cytoplasm is 

 granular, especially in the distal portion of the spindle, and the cell 

 membranes are well marked. 



Very soon the cytoplasm begins to be differentiated, and by the time 

 the pupa has reached the stage figured (fig. 2) vacuoles begin to appear 

 in the proximal end of the spindle, which marks the beginning of the 

 formation of the clear cone substance. The cells now increase in size 

 considerably, and at the same time the number of small vacuoles 

 increases. Later these vacuoles unite, and finally a condition is reached 

 in which the proximal end of each cell is occupied by one large clear 

 vacuole. The cell boundaries remain distinct and a thin layer of 

 granular protoplasm remains surrounding the vacuole, so that it is 

 strictly an internal secretion and not to be interpreted as a secretion 

 poured out on the inner face of each of the cells. This process of differ- 

 entiation or intracellular secretion goes on until the nuclei, which 

 decrease in size and become long and narrow, are pushed to the distal 

 and lateral portion of the cell, where they remain in the adult eye. 

 These nuclei are filled with fine chromatin granules. The cone in the 

 meantime becomes wide at the distal end, and elongates very much to 

 assume its true cone shape, and all that remains of the original cyto- 

 plasm is an extremely thin sheet all around the cone. I am inclined 

 to attribute the descriptions by some authors of nerve fibrils on the 

 cone to the shrinking of this thin film under certain fixatives. There 

 is no nervous connection with the cone, nor does it appear to have any 

 function save transmitting light rays to the sensitive retina. 



There is no indication of any prolongation of the cone proximally, 

 either to form the rhabdome, as previously described, or to form proto- 

 plasmic processes surrounding the rhabdome inside the retinula cells,, 

 such as Patten describes for Vespa. Such fibres could not exist unless- 

 they were to pierce the retinula cells, since the rhabdome is really a. 

 part of the latter; and since the cell boundaries of the cone and retinula 

 are so well marked I feel sure that no such ingrowth occurs. 



Equally unsuccessful has been a search for any additions to the cone 

 at the distal end. In his work on the embryology of the eye of Vespa, 

 Patten describes a layer of cells distal to the cone which arose by an 

 overfolding of the sides of the entire eye, and which gave rise to the 

 lens. In a later paper (1890) he disposes of his invagination theory, but 

 describes a pouring out of chitin from the distal end of the cone, which 

 secretion he mistook for the layer of nuclei at an earlier time. From 

 my examination of Apis material I am unable to find anything which 



