70 BULLETIN OF THE 



(p. 12), "that Graber's cuticula ought to be considered as a connective 

 [-tissue] layer, and in the envelope of the eyes I have been able to estab- 

 lish oval nuclei (PI. II, Fig. 4, nrk) ; and I claim that the pre-retinal layer, 

 which is merged with these membranes, is also of connective nature." 



The conditions of the eye-envelope are somewhat difierently repre- 

 sented in each of Schimkewitsch's three figures illustrating its cellular 

 composition. In one figure (Fig. 4, PI. II) the nuclei appear to lie on 

 the outer surface of the homogeneous membrane; in another (PI. Ill, 

 Fig. 4) they are distinctly on the inner surface ; while in the third (PI. 

 Ill, Fig. 11) they are less definitely related to the membrane, a portion 

 of the nuclei appearing simply as thickenings in it. Figure 4, PL III, 

 is evidently drawn to the largest scale, and also, I believe, represents 

 more truthfully than the others the relations of the nuclei to the mem- 

 brane ; they are simply tangent to the inner surface of the double-contoured 

 membrane. I believe they are without the least doiibt the nuclei of the cells 

 which constitute the posterior of the two layers resulting from the involution 

 of the hypodermis to form the retina. 



"With this explanation of the nuclei supposed to lie in the " sclera," 

 the theory of the connective-tissue nature of the " internal cuticula " is 

 deprived of an apparently valuable support, and now seems to rest on 

 quite as unsatisfactory evidence as ever before. 



Lowne ('84, p. 415) believes that "the columnar cells immediately be- 

 neath the cornea (Grenacher's vitreous) represent the dioptron." " They 

 are separated from the retina by a fibrous membrane which apparently 

 corresponds to the membrana basilaris of tlie compound eye." This 

 basilar membrane the author has previously defined as a cuticular struct- 

 ure. But it is evident from the context that the author rests his conclu- 

 sions on the peculiar fibrous pre-baciUar layer which is found in Salticus, 

 and which Grenacher ('78, p. 51) considered to be composed of fibres 

 from the anterior ends of the retinal cells. Lowne, it is true, denies the 

 direct connection (claimed by Grenacher) of these fibres with the marginal 

 ring of nuclei ; and adds : " In some of these sections the fibrous mem- 

 brane has completely separated from the bacilla, just as the membrana 

 basilaris separates from the retina in the compound eye." It should be 

 remembered, however, that Grenacher also found nuclei in this fibrous 

 layer, and that Lowne's statement in no way affects the validity of that 

 observation,* nor does he (Lowne) attempt any explanation of the fact. 



* From the examination of sections of the eyes of an adult Salticus made by Mr. 

 Locy, and of those of Theiidium tepiilariorum, C. Koch, by Mr. G. H. Parker, I am 

 able to confirm Grenacher's observation. 



