FROM THE MERGUI ARCHIPELAGO. 



265 



lias figured* and described two kinds of retinal cells : (1) pig- 

 mented cells pigmented throughout their whole length, and (2) 

 clear cells entirely tree from pigment. The very small size of 

 the pigmented cells causes the eye of Chloeia to resemble more 

 nearly that of the Alciopidae (presuming that the pigment-layer 

 is really contained in separate cells in the Alciopidae); Chloeia is, 

 in fact, in this particular intermediate between Nereis and the 

 Alciopidae. 



Carriere did not find, or at least does not figure, any rods 

 attached to the extremity of the retinal cells in Nereis ; the 

 whole of the interior of the eye is filled with a plug of tissue 

 termed by him the vitreous body (G-allertkorper). Patten t 

 suggests, with apparent reason, that part of this, at any rate, is 

 in all probability composed of a layer of rods. If this is not 

 the case, the eye of Nereis differs in a very striking fashion 

 from the eye of Chloeia and the Alciopidae J. The retinal layer 

 is continuous anteriorly with a delicate layer of cells, the eve 

 being therefore, as in other Annelids, a closed sac. There is 

 not, however, a space left in the eye between the retinal layer 

 and the vitreous layer ; the w r hole of the available space is 

 occupied by a lens which has rather a peculiar shape, as shown 

 in fig. 8 of Plate XXI. ; this lens is deeply stained by borax 

 carmine. In that particular, and in its laminated structure, it 

 agrees exactly with the cuticle which covers the eye externally ; 

 the structure of the lens, in fact, appears to be closely similar to 

 that of the Alciopidse §, and to differ from that of Nereis. In 

 the Alciopidae a considerable space is left between the lens and 

 the extremities of the rods ; there is no such space in Chloeia, 

 the lens being nearly in contact with the rods (PI. XXI. fig. 6) ; 

 in this particular, therefore, it resembles the lens of Nereis. 



An important feature in the eye of Chloeia is the continuity of 

 the cuticle and the lens. A careful examination of consecutive 

 sections showed plainly that there is no break whatever between 

 the cuticle, which covers the eye externally, and the lens ; the 

 latter appears to be simply a thickening of the former. I am 

 not disposed to deny that the connection between the lens and 



* Loc. cit. p. 31 et seq. 



t Greeff, " Untersuchungen iiber die Alciopiden," Nov. Act. Acad. Leopold. - 

 Carol. Bd. xxxix. (1876). 

 ; Mitth. a. d. Zool. Stat, zu Neapel, Bd. vi. (1886), p. 701. 

 § Greeff, loc. cit. 



