46 bulletin: museum of comparative zoology. 



gewinnen." Through this turning the "urs|)runghch abwiirts ge- 

 richteten Eintrittsstellen der Nerven in die Retina" came to assume 

 a more lateral and superficial position, and so the more or less dis- 

 tinctly inverse form of the eyes has arisen. We must admit that 

 the parts of the eye do not begin their development in the positions 

 which they come to occupy in the adult ; but in Eucalanus the change 

 has not brought about inversion of the retinal cells. Hesse (:01, 

 p. 353) takes a view similar to that of Claus. He is of opinion that 

 the inversion of the median eye of Crustacea occurs because visual 

 cells, which have migrated out of the epidermis, have become oriented, 

 for physiological reasons, with the sensitive portions directed toward 

 the pigment ; later the cup about the cells is formed by the incurving 

 of the pigmented shell. It is probable that the relative positions of 

 the ventral and lateral ocelli are to be interpreted as indicating that 

 the lateral eyes in such forms as the Pontellidae are originally portions 

 of the median eye. Leuckart ('59, p. 260) seems to be of the opinion 

 that the eyes of Anomalocera, which are provided with lenses, are 

 independent of the median eye, in the sense that the latter is the equiva- 

 lent of the eye of Cyclops. Claus ('59) at first accejited this view, 

 but later ('63, p. 46) was led to believe that the lateral eyes of Pon- 

 tellidae might be considered as originally belonging to the median eye. 

 In a subsequent paper (Claus, '91, p. 247), however, he again adopted 

 the interpretation of Leuckart and states (p. 250) that the dorsal eyes 

 of the Pontellidae must be very different from the median eyes, and 

 are to be homologizeil with the compound, facetted, eyes of Arthropoda. 



Parker ('91) has shown that the lens eyes of Pontella are entirely 

 separated from the body ectoderm, while the compound eyes of the 

 Decapoda are continuous with the hypodermis. Those of the Clado- 

 cera and Branchiopodidae are of an intermediate type. Hesse ('02, 

 has adopted a similar classification as regards the higher Crustacea 

 and Arthropoda in general. With this I agree, and consequently, I 

 think we cannot adopt the view of Claus ('91, p. 250), that "Wir 

 liaben also die interessante Thatsache zu constatiren, class auch unter 

 den Copepoden [Pontelliden] das bei den Phyllopoden und auch Cirri- 

 pedien schon so hoch entwickelte zusammengestzte iVugenpaar vertoe- 

 ten ist." Whether the lens eyes of Pontella are compound or not, 

 they must be looked upon as of an entirely difl^erent type from those 

 of the Decopoda or Phvllopoda and Cladocera. 



But as regards Eucalanus, the conclusion seems to me to be warranted 

 that the lateral ocelli are subepidermal and, in that particular, of the 

 same type as the lateral eyes of Pontella. The axes of the cups are 



