60 , W. J. DAKIN. 



only difference was in the number of cells present ; they were 

 apparently as large as usual but fewer in number. These 

 eyes, in fact, appeared to be young ones, or rather, they had 

 been arrested in development and had remained with the 

 small number of component cells characteristic of young eyes, 

 though they were just as old as the large ones. 



In examining hundreds of eyes one meets some strange 

 abnormalities, though the latter are of rather rare occurrence. 

 In a specimen of P. opercularis two eyes were fused 

 together so that the pupil was oval with a slight constriction 

 indicating the boundary of the separate organs. Often the 

 eyes appeared with very little black pigment — that is, all the 

 eyes of a specimen, even the " iris " cells being almost un- 

 pigmented. 



I never found any of the eyes completely covered with 

 pigment as stated by Patten, nor has this feature been met 

 with by any of his successors. 



General Structure of Eye-Stalk. 



The eyes are situated at the ends of short stalks (PI. 6, 

 fig. 1), which, as already pointed out, Avere considered by 

 Poli as modified tentacles. This eye-stalk is made up of 

 connective tissue, which is a direct continuation of that of the 

 mantle-edge and is clothed by an epithelial layer, also a direct 

 continuation of the pallial epithelium. 



The connective tissue is more homogeneous or hyaline in 

 appearance than that of the tentacles, and is not broken up 

 so much by crossing muscle-fibres, which, as might be ex- 

 pected, are a prominent feature of the retractile tentacles. 

 This homogeneous tissue extends also below the eye-stalk for 

 some distance, and the transverse muscle-fibres Avhich raise 

 the velum are absent under the eyes, being arranged in 

 bundles situated between these sense-organs. Large blood- 

 spaces occur irregularly scattered in the stalk, communicating 

 with one another and usually containing blood-corpuscles 

 (PI. 6, fig. 1, Lac). There is, however, scarcely such a 



