106 BULLETIN OF THE 



Gonodactylus (Fig. 101) the retinular cells are certainly as numerous 

 as in Squilla ; but seven obvious cells in the retinula, as I have already 

 shown in Mysis, may suggest the presence of eight in all, one of them 

 being rudimentary. This condition is in fact characteristic of Gonodac- 

 tylus also, as can be seen in the series of ommatidia shown in Fig. 100. 

 These six ommatidia repi'esent consecutive individuals in one of the 

 bands of larger ommatidia previously mentioned. The band as a whole 

 is cut obliquely, and in such a way that the ommatidia from 1 to 6 are 

 cut successively in deeper or more proximal planes. In ommatidium 1 

 the rhabdome is surrounded by seven retinular cells, four of which are 

 upon the right side and three upon the left. In addition to these, a 

 large nucleus (nl. px.) lies close to the rhabdome. Ommatidium 2 has 

 essentially the same structure as ommatidium 1. In ommatidium 3 the 

 nucleus corresponding to the one seen in ommatidium 1 and 2 is no longer 

 visible, but in its stead there is a small mass of granular protoplasm. 

 A similar mass is also seen in ommatidia 5 and 6. It is usual!}' pres- 

 ent directly proximal to the nucleus figured in ommatidia 1 and 2, and 

 is, I believe, the protoplasmic body of the cell to which this nucleus 

 belongs. In ommatidium 4, the seven nuclei of the seven large (func- 

 tional) retinular cells can be seen. These nuclei appear very large in 

 transverse section compared with the cells in which they occur. It is 

 probable that the cell wall is distended by them, although, owing to the 

 indistinctness of the cell boundaries, I hiive not obtained positive evi- 

 dence of this. In ommatidium 6 the seven retinular cells are seen in 

 section at a plane proximal to that in which their nuclei lie. As in 

 ommatidium 1, three of them are upon one side of the rhabdome 

 and four upon the other. In a part of the ommatidium more proxi- 

 mal than that shown in number 6 (Fig. 100), the transverse section 

 of the retinula has the appearance seen in Figure 101. Here the 

 retinular cells have the same relation to the rhabdome that they do in 

 ommatidium 6 (Fig. 100), except in the case of the upper right-hand 

 cell of that figure. This cell enlarges in its more proximal portion, and 

 comes to occupy a position directly below the cell whose nucleus is shown 

 in ommatidium 1 (Fig. 100). The gradual disappearance of this distal 

 cell as one proceeds in a proximal direction from the plane of number 

 6, Figure 100, to that of Figure 101, and the gradual shifting in the 

 position of the cell which replaces it proximally, can be followed so 

 easily that there is not the least question as to the accuracy of the 

 relations described. It is evident, then, that in Gonodactylus, as in Mysis, 

 the retinula consists of eight cells, one of which is rudimentary. 



