48 bulletin: museum of comparative zoology. 



Sehorgane mit Phaosomen ist also eine sehr geringe, so gering, dass 

 wir sagen konnen in fast alien Sehorganen wiirden die Liclitreeipi- 

 renden Endeinrichtungen der Sehzellen durcli freie Nenrofibnlle- 

 nenden gebildet" (Hesse, :02, pp. 609, 610). This author also states 

 (pp. 608, 609), that the most evident ground for assuming that the 

 phaosomes play an essential part in the visual cells, lies in their constant 

 occurrence in those cells only which may rightly be considered as 

 visual cells. Further, as the first of the above quotations shows, he 

 thinks, it may be assumed that neurofibrillae are present in the visual 

 cells with phaosomes as they are in all other cells of the nervous system. 



I have given my reasons for concluding that free nerve endings- 

 occur in the sensory cells of the median eye of Eucalanus, but I tlo 

 not agree with Hesse (:01) in his statement that the endings are of the 

 widespread type which he calls the " Stiftchensaum." It would be 

 presumptuous to doubt the occurrence of this structure (Stiftchen- 

 saum) in the other forms in which he states that it is found, but one 

 may infer from my results that a possible reason for the non-occur- 

 rence of a "Stiftchensaum" in Eucalanus is that Phaosomes are 

 present. At any rate, I can see no reason for not regarding the 

 "interior bodies" as phaosomes, and Hesse himself (:02, p. 609) 

 states that the intracellular, bandlike bodies in the visual cells of 

 several Calanidae are comparable to phaosomes. 



There is also reason for believing that the phaosomes are intimately 

 connected with the transformation of the energy of light into that of 

 the nervous impluse. The club-shaped ends of the neurofibrils have 

 been seen in some cases to lie in contact with the ])haosomes, and the 

 latter have in general a striking arrangement within the cells, more 

 or less conformable to the courses of the nerves. We may infer, then, 

 that there is more reason for assigning to the phaosomes an important 

 role in the visual cells, than simply that they constantly occur there. 

 It seems not improbable that the phaosomes are, in a way, comparable 

 to the rhabdome of higher Crustacea, for it is well known that in the 

 decapods the optic nerve fibres terminate in the rhabdome (Parker, 

 '95, p. 20). Hesse (:01, p. 435) regards the rhabdome of Astacus as 

 composed of the seven modified "Stiftchensliumen" of the seven 

 retinular cells, and Parker ('91, p. 81) is of the opinion that the "rod- 

 like bodies" in the retina of Pontella probably represent rhabdomeres. 



It would be interesting if it could be shown that the median eye in 

 Copepoda is a forerunner of the compound eyes. It is not absurd 

 to look upon the epithelial character of the ventral portion of the 

 median eye as pointing in this direction. The possession of phao- 



