2o6 ANDREWS. [Vol. VII. 



in the pigment mass, but a tendency of this to break up into a 

 few smaller masses, suggesting that it is in as many cells. 



Provisionally, these eye-spots may be interpreted as having 

 the same structure as the larval eyes hitherto considered. 



In the adult Lepraea no eyes were found, so that these larval 

 eyes seem to disappear; yet it is possible that these young 

 belong to some other member of the Terebellidae. 



The foregoing observations upon the formation of eyes in the 

 Polychaetas leaves much to be inferred regarding their cell struc- 

 ture ; yet this is unfortunately true of most of the previous pub- 

 lications upon this subject, as will appear from the following 

 review. 



With reference to the formation of eyes in the budding sylli- 

 didae, it is interesting to note that Albert (14) has described 

 pigment spots in Haplosyllis spongicola Gr. closely resembling 

 the earliest stages in the formation of the sexual eyes in Pro- 

 caerea (Fig. 65). Though no sexual head nor brain is formed in 

 the epitoke or reproductive part of the animal, there are in this 

 separable, free-swimming region many pairs of pigment spots, 

 one on the dorsal base of each parapodium. Each is a collec- 

 tion of elongated, pigmented epidermal cells forming a convex 

 elevation. Each cell has a clear end next the cuticle, these 

 collectively making a " lens." The author regards these organs 

 as the homologues of head eyes, and supposes that they repre- 

 sent eyes in an arrested stage of development, since they have 

 no optic nerve, and so cannot function as eyes. 



Larval eyes are represented by Salensky (16) for Pileolaria, 

 Aricia, and Terebella. In sections they appear as pigment 

 cups from which project clear lenses that may reach up to the 

 cuticle much as in Figs. 59, 66. There is, however, a clear 

 nucleus figured in the lens. 



No special description of the eyes is given, and these nuclei 

 may possibly be merely those of surrounding cells projected out 

 of their true plane on to the lens. 



Meyer (17) has given much more detailed representations of 

 the larval eyes of Psygmobranchns protensus. Each eye is a 

 pigment cup in a thickening of the ectoblast, and contains a 

 clear lens passing from the cup to the cuticle. Later the cup 

 elongates, becomes conical or urn-shaped, and the lens looses 

 its contact with the cuticle. The arrangement of nuclei about 



