MUSEUM OF COMPARATIVE ZOOLOGY. 11 



nent of this view, Patten ('86, p. 670) has claimed that the cone-cells 

 and rhabdome were continuous, and in fact that the rhabdome of the 

 compound eye was only an enlargement of the proximal end of the cone- 

 cell. Kingsley ('86, p. 863) in his description of the eye in Crangon 

 supported Patten's view. 



Of those authors who maintain the separateness of the cone-cells and 

 rhabdome, no one, I believe, has given a fully satisfactory account of the 

 ■way in which the proximal ends of the cone-cells terminate. Grenacher, 

 in describing the eye in Paleemon said ('79, p. 123) : " Die fein ausge- 

 zogene Spitze dieser Pyramide [the cone-cells] durchsetzt, bevor sie in 

 contact niit der Retinula tritt, zuerst eine in Form eines Hohlcylinders 

 sie umhlillende Pigmentmasse um sich dann in das Vorderende der 

 Retinula eine Strecke weit einzusenken." A more detailed account was 

 given by Schultze, who, after stating ('68, p. 10) that in some crusta- 

 ceans the cone-cells appeared to terminate a little in front of the distal 

 end of the rhabdome, said that in the crayfish "geht der Kxystallkegel 

 nach unten in vier Spitzen aus, welche sich aus den vier Kanten der 

 Oberflache entwickeln und das obere Ende des nervosen ebenfalls vier- 

 kantigen Sehstabes umschliessen. Die vier Spitzen legen sich dabei an 

 die Kanten des letzteren an und laufen als lange feine Fiiden auf der 

 Oberflache des Sehstabes herab, diesen umklammernd und mit ihm ober- 

 flachlich verbunden aber durch INIaceration isolirbar. Gegen das Ende 

 spitzen sie sich fein zu und verlieren sich auf der Oberflache des Korpers, 

 den sie umfassen." This account is the most complete of any that I 

 have seen, and yet that Schultze w^as not fully satisfied that he had seen 

 the proximal termination of the cone-cells is probable from the fact that 

 he says the fibres are lost on the surface of the rhabdome. 



The relation of the rhabdome to the cone-cells, and the way in which 

 these cells terminate in the lobster, is as follows. As in other Deca- 

 pods, each ommatidium in the eye of the lobster contains four crystalline 

 cone-cells. Together these cells form an elongated pyramid, with its 

 base next the corneal hypodermis aud its apox on the basement mem- 

 brane (Fig. 1, cl. con.). At the distal end of the ommatidium, in the 

 region which corresponds to the base of the pyramid, tlie four cells 

 are closely applied to each other. This condition is maintained till 

 the deeper part of the ommatidium is reached. Here the four cells, 

 reduced to fibres, separate and end independently on the basement 

 membi'ane. 



A transvei'se section of the distal ends of the cone-cells is shown in 

 Figure 4. On the external faces of each group of four cells there is a 



