298 ASAJIRO OKA; ON SOME NEW 



small and the eirg-cells are scarcely larger than the cells of the ovarian 

 wall, while the spermatozoa are already distinctly formed. 



Tlie eijes. The structure of the eyes of OrohdcUa agrees almost 

 in every point with that of Mucrohddla communicated by Miss Merrill 

 (1894). "The visual cells are arranged in a single layer around the 

 axial nerve-fibres. The symmetry of this arrangement is broken at the 

 upper end and on one side by a multiplication of the visual cells, so 



that the layer there may be two or three cells thick The visual 



cells contain a large crescentic or horse-shoe shaped vacuole surrounded 

 by a layer of protoplasm, in the most thickened part of which the 

 small nucleus is placed, as first pointed out by Prof. Whitman. The 



visual cells are surrounded by the ])igment layer Over the top 



and at the side of the pigment cup, the epidermal cells become 

 elongated to two or three times their normal length." 



As indicated in the figure, the nerve is divided into two l)ranches 

 before it enters the eye. One of these branches forms the axis for the 

 visual cells, wliile the otlier runs along the outside of the pigment cup, 

 gives off some fibres to the scattered visual cells and ends in the cells 

 of the epidermal layer. T'his peculiarity was alrendy described by 

 Maier (1892). 



If we examine OroJnlella externally, we find only one pair of 

 eyes, but the sections show that there are 4 pairs of undeveloped eyes 

 beside them, forming in all 5 pairs. It is the second pair that is 

 externally visilile. The 1st, the 3rd, and the 4th pairs of eyes have 

 no pigment at all. The ath pair has a small quantity of pigment, 

 which is sometimes visible externally as minute black dots. The 

 direction of the axis around which the visual cells are arranged is not 

 the same in all of the five pairs. The axes rather radiate from a 

 certain point situated in the front portion of the head-region, as point- 

 ed out by Apathy (1888 a) for the eyes of Hin ulo. 



