E. J. Allen and E. W. Sexton 353 



less frequently large, white irregular patches, which in the Albino stock 

 may be even as large as the eyes in extreme cases. All these different 

 kinds we speak of generally as spots. They are found most frequently in 

 certain definite positions as shown in Diagram 1. 



Diagram 1. 



The most usual position is at a point on the head behind the eye in 

 the mid-lateral line (1 on diagram). The next position in order of 

 frequency is on the top of the head, near the .posterior margin, and in this 

 position the white pigment generally takes the form of a large irregular 

 patch (2 on diagram). Then there are three positions (3, 4 and 5 on 

 diagram) along the line of the posterior margin of the brain, an upper (3) 

 and a lower one (5), and one in the mid-lateral line, at the anterior end 

 of the stomach (4). A sixth position which is of great interest is in the 

 mid-lateral line on the 1st peracon-segment (6). Very occasionally 

 there is a dorsal spot on this same segment (7). The last position 

 calling for special mention is No. 8, immediately below the eye itself. 

 In addition to these positions spots are found occasionally at other points 

 on the head. 



This detached white pigment seems also to occupy different situations 

 as regards depth. Speaking very generally streaks and small spots are 

 usually quite superficial, but the larger spots are somewhat deeply em- 

 bedded in the tissue. The spots 1, 4 and 6 are usually deep; 3 and 5 

 as a rule deep, 3 being more often so than 5 ; 2 and 7 are superficial. 

 These constantly recurring positions of the white spots seem suggestive, 

 especially the positions of the dorsal patch and of the spots on the 1st 

 peraeon-segment. One thinks at once, in connection with the dorsal 

 spot, of the nauplius eye of crustaceans, which is known to persist in 

 Nebalia. The spot on the 1st peraeon-segment, as well as the two 



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