MUSEUM OF COMPARATIVE ZOOLOGY. 57 



cells, and upon the analogy of the pigment -cells surrounding the reti- 

 nulse of the polymeniscous eyes of Insects and Crustacea, which are 

 very generally held to be of the nature of connective tissue, as also upon 

 that of the ' packing-tissue ' to be described below in the central eye of 

 Limulus. 



" We are by no means anxious to maintain that the more epithelium- 

 like cells amongst what we are about to describe as ' intrusive intracap- 

 sular connective tissue ' may not be of distinct origin from other portions 

 of this pigmentiferous framework, and referable to interneural cells of 

 ectodermal nature ; but any such distinctions must be based upon em- 

 bryological facts which we do not possess. In the present state of 

 knowledge it seems most convenient and justifiable to hold that in the 

 central eyes of the Scorpions there are no interneural cells of ectodermal 

 origin, as there are in the lateral eyes, and that their place is taken by 

 intrusive connective tissue" (pp. 191, 192). 



I believe the authors will agree with me that Locy has now furnished 

 the embryological facts which, by a fair use of reasoning from analogy, 

 will allow us to affirm with considerable certainty that at least their 

 " epithelium-like cells " (or, as they have in another place called them, 

 " intracapsular pavement " cells) are not intrusive, but are derived from 

 the ectoderm, — not, it is true, in so simple a manner as one might have 

 imagined by merely comparing them with the conditions (interneural cells) 

 which they have found in the lateral eyes. There is this fundamental 

 diff"erence between their conceptions and those which are now presented 

 to us : in their view the " intracapsular pavement " cells, even if shown 

 by embryology to be derived from the ectoderm, would still be essen- 

 tially interneural cells ; i. e., such as were originally interspersed among the 

 retinal cells (compare their explanation to Fig. 7). But in the present 

 aspect of the case that is not probable ; they are distinctly not comparable 

 with the interneural cells of the lateral eyes, — assuming that the latter 

 are " monostichous," * — but belong to an extra-retinal region of the 

 ectoderm. 



What they are functionally, is to be inferred from their pigmented con- 

 dition. Their position indicates that they are, in addition, the matrix for 

 that portion of the basement membrane which has received the name 

 " sclera." 



Whether the " intracapsular epithelium " represents the xohole of the 

 posterior layer of the infolding, is a question which is intimately con- 



* Whether Lankester and Bourne are right in claiming the lateral eyes of scorpions 

 to be "monostichous," is quite another question, which will be discussed presently. 



