44 bulletin: museum of comparative zoology. 



ends of the cells. And it should be pointed out again that, whether 

 we consider the "central cell" or the "basal plates" as the pigmented 

 portion of the eye, the truth of the previous statement is not affected. 

 In the ventral ocellus of the median eye the basal plates lie beneath 

 the basement membrane of the hypodermis from which the retina is 

 formed. Moreover, it is merely consistent, and warranted by the 

 facts of their structure, to consider that the basal plates of the lateral 

 eyes are at the basal ends of the cells. If the central cell contains the 

 pigment of the eye, as I believe is the case, the "basal" ends of the 

 retinal cells must also be considered their "inner" ends, since in that 

 case they are directed toward the pigment of the eye. 



In the organs of Claus, on the contrary, the nerve leaves the cell 

 from a portion of the periphery opposite to the "basal plate." I can 

 see no reason why the structures in the organs of Claus which I have 

 termed " basal plates" should not be considered the homologues of the 

 similar structures in the lateral eyes. Their appearance and staining 

 reactions in the two places are the same in every way. Consequently, 

 it is only reasonable to look upon that portion of a cell of an organ of 

 Claus which bears the plate as the basal or inner portion. 



If this interpretation is correct, we are forced to regard the organs 

 of Claus as inverted, and as eyes because of the complete correspond- 

 ence in essential features with the cells of the median, nauplius eye. 

 The manner of innervation of these specialized cells in the brain is in 

 accord with the facts recounted by Hesse ('98, p. 483), who says with 

 regard to the eyes in the brain of annelids, "An einzelnen Schnitten 

 konnte ich auch beobachten, wie der ausserhalb des Pigmentbechers 

 gelegene Theil der Sehzelle sich zu einer Nervenfaser auszog." 



It would seem at first thought that a complete correlation between 

 the organs of Claus and the inverted eyes of worms would force the 

 interpretation that the "basal plates" are pigment-bearing structures. 

 But this is not necessarily the case, for it is the position of the plate 

 with regard to the place of exit of the nerve of a cell, which is, as it 

 appears to me, of importance, and not whether the plate may be 

 pigmented or not. If we interpret as broadly as possible the facts of 

 the structure of the median eye, we are compelled to admit that the 

 pigment, wherever it is located, must occupy the same relative posi- 

 tion with regard to the point of exit of the optic nerves as the basal 

 plates. 



Again, the probability that the basal plates of the organs of Claus 

 are not structurally comparable to the pigment-cells of the eye of a 

 planarian, does not in the least militate against looking upon the 



