THE EYE OF PECTEN. 65 



appeared well preserved and very little contraction had taken 

 place. The processes were very definite, and had I found 

 them by other confirming methods I should not have 

 hesitated to describe them as actual cell processes. I have 

 figured, however, the prepai-ation, and prefer to leave the 

 question of their true nature open. The type of cornea just 

 described is that of Pecten jacobseus, P. maximus, and 

 P. opercularis. 



Rawitz ([25], p. 108) divides the types of cornea into three 

 classes : (1) Cells of cornea considerably smaller than those 

 of the pigment-mantle, ex. P. flexuosus, P. glaber, and 

 P. opercularis; (2) cells of cornea, smaller at periphery 

 against the pigment-mantle, but rapidly increase towards the 

 centre, where they equal the pigment-cells in height, ex. 

 P. jacobasus and P. varius; (3) corneal cells are as high 

 as cells of the pigment-mantle at periphery, but increase 

 rapidly in height towards the centre, the nucleus lying near 

 the base, ex. P. pusio. I hardly think it advisable to make 

 such a division, since, in the first place, the appearance often 

 varies with the size of the eye, and it is difficult to fix a 

 boundary between the two first groups. The corneal cells of 

 P. jacoba3us are, moreover, not equal in height to those of 

 the pigment-mantle, though they are much higher in com- 

 parison with the same cells in P. maximus. There is, 

 however, a well-marked division in which Pecten pusio 

 and also P. tigrinus can be placed. The latter is figured 

 (PI. 7, fig. 12). In this species the corneal cells are veiy 

 different from those of P. maximus. Those next to the 

 pigment-mantle are of similar size, or smaller than the 

 adjoining pigment-holding cells, but towards the centre 

 the cells increase in height very considerably until they are 

 deeper than the pigment-cells, the height of the corneal cells 

 being double that of the latter. The cell-boundaries are not 

 very distinct, and intercellular bridges are not to be seen. 

 I have been unable to make out any reason for the peculiar 

 difference in these two forms. 



The connective tissue of the eye-stalk has already been 



VOL. 55, PART 1. — NEW SEEIES. 5 



