The Eyes of Dactylopius. 85 



The maniior in wliich tlie lens attains its approximately circular 

 shape is so well illustratod in the instance under consideration that 

 it may be of interest to describe it in a few words. The initial region 

 of greatest growth in the lens and consequently of raost rapid decrease 

 in the length of the corneal hypodermis corresponds to the axial portion 

 of the latter. Here a depression in the corneal hypodermis quickly 

 appears in which rests the developing lens, which is at first oblong 

 wäth slender lateral projections overlapping the iris cells (Fig. 7). 

 It is this concavity which enables the formation of a circular lens. The 

 abaxial corneal hypodermis cells now being the taller extend distad 

 some distance, in the early stages, to the chitin and thus the growing 

 Ions is surrounded on three sides by cells (Fig. 8). In this manner 

 the lenticular substance is secreted in equal quantities on all sides with 

 a more or less spherical body as the result. The iris cells form that 

 part of the lens that projects beyond the lens proper and in a longi- 

 section of the completed eye appears as two horns, one on either side. 



Simultaneously with the beginning of the lens appears the pigment. 

 The increase in the amount of pigment proceeds hand in hand with the 

 increase in the size of the lens, a condition of affairs that naturally 

 niight be expected, since from the very first the lenticular thickening 

 to a certain degree at least must concentrate the rays of light and thus 

 necessitate the protection of the sensitive cells. As mentioned in 

 connection with the description of the adult eye no special pigment 

 cells are present. Even before the pigment appears, that is, about the 

 time when the corneal hypodermis is formed, the retinal nuclei enlarge 

 as though in preparation for the secretory activity of the cells which 

 foUows (Fig. 6). The fine, spherical granules of reddish-brown pig- 

 ment appear on the retinal cells at the very first indication of the lens, 

 but in the iris cells the granules do not appear until the lens is well 

 advanced. With the increase in the size of the lens the amount of 

 pigment also becomes greater until, when the former is completed, 

 the latter is a dense mass extending even to the surrounding hypodermis. 

 With the depositing of the pigment and the formation of the lens the 

 developoment of the eye is completed. 



Summary. 



The main points regarding the eyes of Dactylopius may be briefly 

 summarized thus. 



The adult individual has three pairs of eyes, two accessory and 

 one primary. The latter are beadlike and lie on the lateral surface 



