78 K. KISHINOUYE. 



of hatching, mid at the same, time becomes concave (tig. 54), instead 

 of being convex as heretofore (ûg. 51). 



In the ' Nebenaugen ' — but not in the posterior median eyes — 

 there are f(n-med transverse liars and a circumferential ling (^g'i. 

 51- 54, tai)) of chitinous natiu-e, posterior to the retinal cells and 

 secreted by these cells. These chitinous bodies (the tapetum) are 

 transparent and lightly yellowish by transmitted light and silvery 

 olitterinsf bv reflected liuht. Tlie lens is formed in a similar manner 

 as in the case of the posterior median eyes. The tapetum and the 

 lens are eqntdly secretion products of the ectoderm and both of them 

 are chitinous in nature, liut they are not homologous. The former 

 is produced at the proximal end of the ectoderm cells, while the latter 

 is formed at the distal end. : . 



I know of only two authors who have studied the development 

 of the spider's eyes b)^ recent modes of investigation. They are 

 Locy and Schimkewitch. The results obtained by these authors are 

 not entirely satisfactory. Locy could not find the diHerence in the 

 mode of development between the 1 wo différent types of eye. He 

 says that the 'Nebenaugen' originate in substantially the same way 

 as the anterior median eyes (my posterior median eyes). Moreover 

 he states that the development of the eyes begins by a local thickening 

 of the hypodermis and a backward directed infolding which inverts 

 the thickened region. Schimkewitch says only that the retinal part 

 of the eyes originate from a pyriform eidargement from the brain, 

 upon which the ectoderm invaginates in the form of a ring. 



Patten recently gave a short account of the spider's eyes in an 

 article entitled the " Segmental Sense-organ of Arthropods " in the 

 Journal of Morphology, Vol. IT. ; but his account differs from mine 

 in many jioints, as I have already mentioned. He says that there 

 are segmental sense-organs, homolog(jus with the eyes, at the base 



