1886,] The Arthropod Eye. 865 
discredit on the “ mosaic” theory of the vision of the compound 
eye, a theory that already was too open to objection to be im- 
plicitly accepted. Lastly, a point to be referred to again, Dr. 
be regarded as evolved by a coalescence of ocelli. 
A second important paper on the Arthropod eye has already 
been mentioned in the pages of this magazine, but its connection 
with the subject in hand will excuse its being brought up again. 
5 Though several authors have mentioned facts in the development 
_ ofthe arthropod eye—some, like Bobretzky, giving details of 
_____importance—Mr. Locy was the first to indicate the most import- 
_ ant feature in the process. In his paper entitled “ Observations 
_ On the development of Agelena nevia” (Bulletin Mus. Comp, 
a Zool., x11, pp. 63-103, 12 pls., 1886), he shows that in an early 
= Stage the eyes appear as local thickenings of the epidermis fol- 
lowed by an invagination of these thickened portions which thus 
come to lie beneath the surface. The pouches thus formed, one 
for each eye, are then cut off from the parent layer, and we have 
now to deal with three layers. From the outer (epidermal) arises 
= Was not clearly determined) while the fate of the inner layer 
_ Was not traced. Locy points out that as a result of this mode of 
development, one supposed difference between the eyes of artho- 
pods and those of vertebrates disappears, and the rays of light 
traverse the retinal elements of the one group in exactly the same 
direction with regard to their origin as they do in the other. 
_ Sedgwick (Quart. Jour. Micros. Sci., xxv, 1886) was the first 
to point out that the eye in Peripatus was developed from an in- 
a le epithelium outside the lens of the adult eye, while the inner 
L wall Joins the cerebrum and gives rise to the retina. Hence, says 
_ >edgwick, the eye of Peripatus is a cerebral eye. 
: same genus (Entwicklungsgeschichte von Peripatus, 11 Theil. 
Patten comes to the conclusion that the compound eye can not 
the cuticle, cuticular lens and vitreous body of the adult; from. 
the middle arises the retinal elements of the adult (exactly how. 
Kennel has also studied the development of the eye in the | 
9. z, z. Inst. Würzburg, viii, pp. 1-93, pls. 6, 1886), and gives 
_ APP: 31-33) further details. He too recognizes the invagination, 
Which becomes cut off from the parent layer, but says that its ` : 
aner wall has no close connection with the rudimentary brain, > 
but that ‘the nervous connection with that organ is secondary. _ 
k 
Vagination. The outer wall of this sac is described as forming — a 
pee 
