226 G. M. Giles — Notes on the Amplilpoda of Indian Waters. [No. 3, 



The animal differs from A. gaimardii, A. ingens, A, belliana^ A. 

 limicola, and J., ^opon tea, the species figured by Spence Bate Qoc. cit.)y 

 in the great length of the fifth thoracic appendage ; from A. jpelagica 

 in the antennae being shorter, in its colour being white instead of pale 

 yellow, and in presenting no blotches of red pigment on the cephalon ; 

 from A. macrocephala in the eyes being larger, and the upper and 

 lower pairs equally distinct, in none of the segments being carinate, in 

 colour, and in size ; from A. tenuicornis, A. Icevigata, and A. carinata 

 in wanting the posterior dorsal carina. 



Anatomy. — The visual organs of Ampelisca are arranged in a manner 

 somewhat exceptional amongst the Ampliipoda. Being anxious to 

 examine the minute structure of these and to make out whether both 

 pairs of eyes were alike or of different structure, I made several sets 

 of serial sections in the various axes of the animal. From an examina- 

 tion of these, the following points were made out, which, without pre- 

 tending to be a complete account of the minute anatomy of the animal, 

 it may be well to record. 



Organs of Vision. — The two pairs of eyes are identical in structure, 

 but quite distinct from each other, and belong to a high type of the 

 simple invertebrate eye. The portion of the chitinous coat of the head 

 which forms the " cornea " is but slightly more convex than the general 

 curve of the part. Imbedded in this is a refractile body of a slightly 

 flattened spherical form, consisting of a delicate sac containing a struc- 

 tureless gelatinous material. 



The sac is quite distinct from the cavity in which it is contained, 

 and is capable of dislocation from its hollow bed. In sections where this 

 has happened the contained material may be seen ooziug from the 

 shrunken sac, and forming a drop very similar in appearance to the myelin 

 drops that form in the course of a medullated vertebrate nerve. The 

 lens, thus formed, rests on a concave surface formed of the epidermic 

 layer of the head, which here consists of soft rounded cells, granular 

 and easily stained in spirit specimens, but doubtless quite transparent in 

 life. Surrounding the lens, and forming a sort of iris, is a ring of these 

 epithelial cells, deeply impregnated with a deep brown pigment. 



Behind this epithelial layer comes the retina. This consists of 

 three distinct layers. Immediately beneath the epithelial layer is a 

 layer of cylindrical bodies, nucleated and deeply pigmented, and con- 

 tinuous with the bases of these (so that each appears to have its con- 

 tinuation in the next layer) is a layer of tapering rods, which divide at 

 their deeper extremity into two or more slender fibres. Between these 

 two layers there is doubtless an organic connection, each cylinder 

 fitting accurately on to its corresponding rod, but that the continuity is 



