No. 2.] EYES OF POLYCH^TOUS ANNELIDS. 201 



large, and extend to the ventral face near the base of the palp, 

 right and left. 



Though no later stages were examined, it seems that these 

 eyes disappear, or at least have no connection with the eyes of 

 the adult. 



The four definitive eyes are seen at fifty hours, in Fig. 54; at 

 the first they have a more nearly transverse arrangement than 

 here figured. Each is a collection of red-yellow pigment gran- 

 ules, in every respect like the provisional eye at ten hours. 



By fifty-seven hours the pigment granules are aggregated in 

 a disk-shaped mass which, in maceration, seems to fill the outer 

 end of one cell. These eyes grow quickly, so that at sixty 

 hours the larva has three pairs of nearly equal reddish eye-spots. 



A clear lens appears in each cup, and at seventy hours the 

 posterior eyes still look upward, while the anterior, permanent 

 eyes have turned over, so that they look forward, and present 

 a crescentric outline viewed from above. 



Sections at eighty-four hours give the same structure as in 

 the provisional eyes at fifty (Fig. 59). Macerations lead one 

 to infer that the pigment is in a few cells, in the ends close to 

 the lens. 



At ninety-six hours, the pigment cup has become dark blue, 

 almost black, with a few scattered yellow granules passing 

 inward from it, as seen in the section (Fig. 60). 



At one hundred and fifty-six hours, the eyes are blue or dark 

 red, and contain a prominent lens. Moreover, surface views of 

 the bottom of the cup, seen in tangential sections, reveal minute 

 clear spaces in the dark pigment, as shown in the adult (Fig. 17). 



Larvae one hundred and sixty and two hundred and two hours 

 old are no farther advanced than one only eighty hours old, 

 reared in the warmer climate of Beaufort, N.C. (Fig. 55). Sec- 

 tions of these two periods show stages intermediate between 

 Fig. 60 and Fig. 61. 



This last figure is that of the young Nereis (Fig. 56), and 

 presents an advance, in that the lens and the rods are now 

 distinguishable as two well-defined parts of the refracting mass. 

 Owing to poor preservation, this figure does not approach as 

 near to the adult condition as the eye itself probably does, 

 as indicated by the faint traces of a division of the rod region 

 into separate rods. 



