80 BULLETIN OF THE 



Lenses similar in position to those in Pontella have been identified 

 in the lateral eyes of several other genera of Copepods. Gegenbaiir 

 ('58, p. 71) described such lenses in Sapphiriua, and Leuckart ('59, 

 p. 250) observed similar ones in the lateral eyes of Corycseus and 

 Copilia. In all these genera the lenses, although biconvex, are not 

 spherical, as in Pontella. Gegeubaur ('58, p. 71), following Leydig's 

 generalization, believed that in Sapphirina the lenses were thickenings 

 in the cuticular covering of the body, and Clans ('59, p. 271) considered 

 them morphologically equivalent to a single corneal facet. Leuckart 

 ('59, p. 250),. without definitely committing himself as to the nature 

 of the lens, states that in Copilia and Coryca)us the lens is implanted 

 in the superficial cuticula, and further describes it in Corycseus as com- 

 posed of two parts, an outer and an inner. According to Grenacher 

 ('79, p. 67), both parts can be identified in the lens of Copilia ; the 

 outer part is a portion of the superficial cuticula; the inner part, both 

 in its optical properties and its behavior toward reagents, is unlike the 

 cuticula. The inner part, however, contains no traces of cells, but is 

 composed of a homogeneous substance, probably secreted. This view of 

 the duplicity of the lens contrasts with the older idea of its origin as a 

 thickening in the superficial cuticula. 



It is possible that the lenses in the Pontellidse and Corycseidse are not 

 homologous structures, but on account of their similarity I am inclined 

 to consider them as such. Since in Pontella both parts are derived 

 from the cuticula, I believe that a similar origin will be demonstrated 

 for these parts in the Corycseidse. The differences which Grenacher 

 has pointed out between the two parts of the lens in Copilia do not 

 necessarily oppose this view. It is possible that the cuticular secretion 

 which forms the proximal part of the lens may originate separately 

 from the other cuticula, as in fact it does in Pontella ; and it may also 

 be true, although this is not supported by the condition in Pontella, 

 that the two parts, although both secretions of the hypodermis, may 

 differ enough in their substance to account for all the peculiarities ob- 

 served by Grenacher. 



The retina and lens in Pontella are not separated by an intervening 

 space as in the Corycseidse, but are in immediate contact. The retina 

 is composed of a mass of cells, the number and arrangement of which 

 can be seen in the figures on Plate III. These figures represent a 

 series of consecutive sections cut in planes transverse to the axis of 

 the eye, i. e. parallel to the horizontal plane of the animal (compare 

 Fig. 18, Plate II.). The series is complete in that it represents all 



