esterly: eucalanus. 11 



strable in any of my material, probably because of its solubility in 

 alcohol. Parker ('91, p. 78) has found that in Pontella the pigment 

 dissolves very readily in alcohol, so that all traces of it disappear under 

 this treatment. I can state positively that the eye of Eucalanus 

 elongatus does contain redthsh pigment while the animal is alive, 

 for I have seen it many times, but without noticing closely its location. 

 Giesbrecht ('92, Taf. 3, Fig. 1) has also seen such a condition and has 

 figured it. In view of this comparative evidence, I think it likely that 

 Grenadier has mistaken certain other structures for pigment plates, 

 though it is reasonable to suppose from the general appearance of the 

 objects which he called pigment plates, that they, too, have this func- 

 tion. It should be added here that the cytoplasm of the central 

 cell (Plate 1, Fig. 6, cJ. c.) is of a vacuolated, spongy appearance, while 

 the plates which Grenacher has described are very dense and homo- 

 geneous in appearance, showing no traces of granulation. 



e. Basal Plates. — Plates like those described by Grenacher are very 

 conspicuous objects in the eye of Eucalanus elongatus (Plate 1, Figs. 

 1, 2, 6, 9; Plate 5, Figs. 49, 50, la. ha.), though there are differences 

 between the conditions in this species and those described by Grenacher 

 in E. attenuatus. He states ('79, p. 64) that each of the three portions 

 of the eye has "a special pigment plate." In Eucalanus elongatus, 

 each lateral eye possesses two plates, an anterior and a posterior, which, 

 as I have said, do not contain pigment, if such evidence as has been 

 brought forward is valid. The plates of the lateral ocellus cover the 

 median ventral surface of the ocellus. Each plate is triangular in 

 outline, and conforms to the curvature of the cup; in the natural 

 position of the animal the apex of each triangle is invariably directed 

 ventrally (Plate 2, Figs. 21, 22). The plates are of about equal size, 

 and in general the dorsal margins of the two together extend around 

 the median half of the eye (Plate 1, Figs. 1,2). The anterior and pos- 

 terior plates approach each other, but are never in contact, so far as I 

 have seen. The point where they most nearly touch lies approxi- 

 mately in the mid-transverse plane of the eye. 



As seen in cross sections of the eye, each plate occupies what may 

 be termed the ventro-median third of each lateral eye (Plate 1, Fig. 9). 

 The extent of the plate in such a section is practically the same as the 

 tapetum on that face of the central cell (Plate 2, Fig. 16; Plate 5, 

 Figs. 49, 50). In frontal sections (Plate 1, Fig. 2; la. ha. and lap.) 

 it may be seen that in an antero-posterior direction also the tapetum 

 is practically co-extensive with the plates. 



The plate of the ventral eye (Plate 1, Fig. 6, Plate 5, Figs. 49, 50, 



