552 William Patten 



p.367, »Obgleich iu dem Baue dieser Augen manches Eigen- 

 thümliche besteht, so stimmen sie doch im Wesentlichen 

 mit den Sehorganen anderer Mollusken überein«. This 

 Statement indicates more faith in the uniformity of structure of Mollus- 

 can eyes, than actual Observation. 



These are the only remarks upon the eyes of Area , to my know- 

 ledge, up to 1883, when Carrière published an imperfect and inaccu- 

 rate description of the eyes of Area and Pectwieulus , in which he 

 falls to add anything new to the subject. At the same time, he ex- 

 poses himself to the charge of plagiarism, for be lays special stress 

 on the fact that the eyes of Area are compound, or »fan eyes« as 

 he calls them , and passes over in silence the fact, that Will had 

 long ago fully recognized the same — which has not been mentioued 

 by any recent author, — iu an article no longer easily accessible. 

 He has, moreover, produced drawings of sections, cut with a mo- 

 dem microtome and prepared with ali the help modem histological 

 technique can give, in which he has represented, and also described in 

 the text, the eyes as being formed simply of cone-shaped cells coated 

 with pigment, each one being provided with a lens-like thickening of 

 the cuticula. A reference to my own drawings will give an idea of how 

 accurate I consider bis descriptions to be. Such Observation» are of 

 double harm, for they not only introduce false notions into science, but 

 disarm suspicion , coming , as they do . from one who has made a spe- 

 cialty of the subject, and who is, presumably, equipped with a tech- 

 nique, which should euable him to keep pace with the progress of mo- 

 dem histological research. 



The compound eyes , as we bave already said, consist of from 

 10 to 80 ommatidia, and measure from .07, to .14mmin diameter. 

 Each ommatidium consists of a centrai, colorless core, formed of two 

 fused cells , whose bases are directed outward and support a double, 

 highly refractive, and transparent rod. The centrai cells, or retino- 

 phorae as we shall cali them, are surrounded by eight pigmented 

 cover cells, or retinulae, arranged in two rows of four each, one 

 above the other (PI. 30, fig. 59) . The whole ommatidium, which is about 

 .04 mm long, is wedge-shaped, the apex being directed inward. In 

 order to obtaiu a good idea of the structure of these compound eyes, 

 it is necessary to resort to some macerating fluid in order to separate 

 the different cells ; if the maceration is stopped at different stages of 



