THE COPEPODA 85 



part of the ocular apparatus reaches back into the region of the 

 anterior thoracic somites, and in Copilia the pigment-cups enclos- 

 ing the retinal cells lie together in a conical protuberance on the 

 sternal surface of the body. 



In this account it has been assumed that the " paired eyes " of 

 Pontellidae and Corycaeidae are derived from the dorso- lateral 

 elements of the nauplius-eye. It must be mentioned, however, 

 that Glaus, while admitting this derivation in the case of the 

 Corycaeidae, regarded the lateral eyes of the Pontellidae as homo- 

 logous with the paired compound eyes of other Crustacea. If it be 

 the case, however, that in the Pontellid eye, as in those of other 

 Eucopepoda, the retinal cells are "inverted" (or are connected 

 with nerve -fibrils at the end turned towards the light), this 

 homology would seem to be impossible. 



A problematical organ to which a visual function has been 

 attributed is found in the genus Pleuromamma. It lies on one side 



FIG. 47. 



Corycaeus anglicus, male, from the side, showing one of the large paired eyes. I, lens ; c, 

 crystalline body ; p, tubular pigment-cup. (After Leuckart) 



of the Cbpuajic siiieid, in the region of the maxillipeds, and consists 

 of a globular refractive body enclosed in a mass of pigment, the 

 whole projecting from the surface of the body in a little papilliform 

 elevation. It has also been suggested that this is an organ of 

 phosphorescence, but according to Giesbrecht this is not the case. 



The " aesthetascs" or "olfactory filaments," of the antennules 

 have already been mentioned. Their number and arrangement 

 vary very much in different forms, and afford valuable systematic 

 characters. 



The "frontal sense-organs" are certain sensory setae, generally 

 a single pair, on the front surface of the head above the rostrum, 

 which are supplied by a pair of nerves arising from the brain, 

 and which have been supposed to be the seat of some special 

 sense. 



The existence of " auditory " organs in the Eucopepoda is 

 doubtful. A pair of statocysts have been described in the 

 anterior part of the brain in Eucalanus. 



