80 



gives oil a fine branch to the ink gland at the level where 



the ink duct enters the intestine. It has not, however, 

 been followed in Eledone. Front the posterior edg-e of the 

 gastric ganglion are given oft' several small nerves to the 

 initial par! of the intestine and spiral caecum, and also a 

 large branching nerve to the postero-ventra] wall of the 

 stomach (fig. 73, d). 



SENSE ORGANS. 



The general surface of the body of Eledone is sensory, 

 the arms in particular forming slender sensory organs. 

 There are, in addition, well developed eyes, organs of 

 equilibration — the statocysts, and the olfactory organs 

 which probably function also as taste organs. 



The Eye. 



Eledone has a pair of prominent eyes, situated one. 

 on each side of the head (PI. T, fig. 1, E.). As ill the case 

 of most Oephalopods, they are sessile. In large specimens 

 of E. eirrosa the diameter of the eye is about 25 mm. 

 Although it much resembles the vertebrate eye in several 

 respects, i.e., both are vesiculate and both are very 

 complex and remarkably perfect in structure, yet there 

 are many profound differences. The eye of Eledone has 

 no anterior or aqueous chamber, no choroid, and the cells 

 of the retina are different from those of the vertebrate 

 retina. Again, while the Vertebrate has a cerebral eye, 

 that of Eledone originates as an invagination of the 

 epidermis, which later becomes elaborated into retina, 

 iris, &c. Another important point upon which they differ 

 is that while in vertebrates the optic nerve penetrates 

 the retina and enters the retinal cells from the front, in 



