ANTENNATA SENSORY ORGANS 



471 



called retinophorse. The crystalline cones are the elements actually sensitive to light. 

 The retinophor?e are surrounded by pigment cells. A proximal (inner) ring of these 

 cells corresponds with the so-called retinulse, but these cells are also continued in the 

 form of fine processes as far as the hypodermis. Fig. 329, A, illustrates this view. 

 The layer of single eyes is said to answer- 

 to the posterior wall of a vesicular eye, 

 which first forms as an ectodermal de- 

 pression and later becomes constricted off. 

 The whole compound eye would according 

 to this be a modified and differentiated 

 ocellus, in which the epithelial cells of the 

 posterior proximal wall of the eye -pit 

 differentiate into retinophone and pigment 

 cells, grouped together as ommatidia (as in 

 the middle eye of the Scorpion). The 

 hypodermis, further, which spreads over 

 the vesicular eye, instead of forming one 

 cuticular lens, forms many such lenses, 

 which as corneal facets correspond in 

 number and position with the ommatidia. 

 The ocelli themselves may also be compared 

 with the similarly constructed visual organs 

 in the Annelida and Mollusca which arise 

 as ectodermal invaginations. 



If this new view of the facet eye is 

 established, i.e. if the so-called crystalline 

 cones are not simply refractive bodies, but 

 the actual terminal apparatus of the optic 

 nerve, sensitive to light, it would lead to 

 considerable modification of the theory of 

 sight by means of the compound eye. 



B. Auditory Organs. 



FIG. 329. The structure of an omma- 

 tidium (single eye) of the facet eye. A, 

 According to Patten's view. B, according 

 to Grenacher's view, cl, Cuticular corneal 



nuclei of the same ; k, crystalline cone ; p, 

 pigment cells ; ret, retinulae ; rh, rhabdome ; 

 71, nerve. According to Patten (A) the 

 ommatidium is, apart from the corneal 

 hypodermis, of one layer, all its elements 



In the most Various parts Of the lens ; Jiy, hypodermis cells of the corneal 

 bodies of the Insecta peculiar nerve lenses; r^retinophora = crystal cells; nr, 



endings occur which are evidently 

 sensory ; their structure is as follows : 

 A peripheral nerve fibre enters a 



1 . !_'!,* * "j-J. 



ganghomc cell, which is in its turn passing by means of thin pr0 cesses through 



Connected with the integument by its whole thickness from the base to the 



means of a long slender stretched Z^' S^fSSfZ 

 tube. An axial thread irom the consists of two layers. 

 ganglionic cell enters the tube, and 



there ends in a terminal rod. The tube which conceals this rod is 

 called the seolopophore, and that part of it which becomes attached 

 to the integument is the terminal tube. Scolopophores with their 

 ganglia are rarely found singly, they are usually united in groups of 

 varying size (Figs. 330, 331, and 332). If the number of scolopo- 

 phores is small their terminal tubes are gathered into a bundle, but if 



