36 bulletin: museum of comparative zoology. 



27, 35; Plate 6, Fig. 56). They are in the closest apposition with the 

 great nerves {n. at.) which supply the first antennae, and they lie on 

 the median side of these nerves, but have no connection with them. 



b. Com.'position . — In entire preparations and on cursory examina- 

 tion of sections, the structures may really appear to be vesicles, as 

 Claus said; but closer inspection shows that each organ is composed of 

 two large cells of about equal size, which are so much flattened against 

 each other that they together form an approximately spherical body. 

 Each cell contains a fairly large nucleus (Plate 2, Fig. 20; Plate 3, 

 Figs. 31, 33) with chromatin in the form of a network. A comparison 

 of the dimensions of nuclei and cells in the brain proper with those 

 of the organs of Claus, shows that, while the nucleus of a brain cell, 

 on the average, is a little larger than a nucleus of one of the cells in an 

 organ of Claus, the cells of the latter are several times as large as the 

 cells of the brain. The average diameter of nuclei in the cells of the 

 brain is approximately 9.1 ji, while the nuclei of Claus's organ are on 

 the average not over 8.5 ix in dianieter. The average diameter of the 

 cells in the brain is 11.7 ix, while the cells in the organs of Claus average 

 30 [X in diameter. These values have been obtained by careful meas- 

 urement of cells and nuclei both in whole preparations and in sections 

 cut in three planes. 



c. Similar iti] in Structure to the Cells of the Median Eye. — The 

 most striking thing about the cells of the organs of Claus is their 

 resemblance to the cells of the median eye. It may be said that, 

 within certain limits, to be later defined, a cell of an organ of Claus 

 corresponds in every way with a retinal cell of the median eye. Each 

 of the two cells in Claus's organ is provided with a structure which is 

 an exact counterpart of the basal plate in the median eye. It becomes 

 red in ]\Iallorv's stain (Plate 5, Fig. 55, la. ba.) and brown or black in 

 vom Path's mixture (Plate 2, Figs. 11, 12,7a. ba.). But in the median 

 eye, a basal plate is shared by several cells, whereas in the organs of 

 Claus each cell has formed its own basal plate, which covers a portion 

 of the periphery of the cell. Sections cut in the three principal planes, 

 and whole preparations, show that the basal plate measured in any 

 direction occupies about one-third of the entire periphery of its cell 

 (cf. Plate 5, Fig. 55, Plate 2, Figs. 18 and 20). As in the case of the 

 median eye, the basal plate of the organ of Claus possesses no intrinsic 

 structure. The region of the cells Occupied by the basal plates is 

 also, in part, the region in which the cells are in contact. This gives 

 rise to an appearance in darkly stained vom Rath material (shown, 

 for example, in Plate 2, Fig. 12 and Plate 3, Fig. 36) which suggests 



