274 E. J. ALLEN AND E. W. SEXTON. 
pigment of the eye was replaced by a bright red pigment.* It was shown 
that these red eyes behaved as a pure recessive in accordance with 
Mendel’s law, the hybrid between red-eyed and pure black-eyed animals 
being black. Certain other mutations which had just occurred were 
also described and figured in that paper, and it is to a study of these 
and of others that have since appeared that the present paper is due. 
Our thanks are due to Miss A. R. Clark, who has given valuable help 
in the care of the broods and in the examination of the young animals 
for eye-colour. 
The system employed for designating the different broods and the 
individual animals in each brood is as follows: The two original Albino 
females from which the experiments started are called AB and AC. 
The five broods obtained from AC are numbered I to V, the one brood 
from AB is numbered VI. Each animal which came to maturity in each 
of these broods is designated by a capital letter, A, B, C, ete. Hach 
brood derived from one of these females is numbered by an arabic numeral, 
and each animal in the brood is denoted by a small letter, a, b, ¢, ete. 
Thus I.K.3.a. means the first individual (a) in the third brood (3), of female 
K from brood I of the original female AC. (See Plate I.) 
In the plates the colour developed in the eye of each animal is shown 
by the large circles, and the constitution of the animal in regard to the 
factors for eye-colour, when known, by the character and position of the 
small circles. The V-shaped mark indicates that the presence or absence 
of the factor usually represented in the position where the mark stands 
has not been proved. 
In the text the colours are represented by capital letters. A means 
albino, B black, R red and N no-white. The first letter in a formula in 
black type gives the visible colour of the eye, the remaining letters the 
constitutional factors which are carried. Thus B+R+A means a black- 
eyed animal, carrying the factors for red and albino, B-+-N means a 
black-eyed animal carrying the factor for no-white. BN and RN mean 
black and red no-white respectively. 
SECTION I. THE ALBINO} IMPERFECT EYE 
The shape of the normal eye of Gammarus chevreuri 1s voter with 
the margin entire. (Plate VII. Fig. 2.) The eye is raised above the 
surface of the cephalon, and much rounded, and is composed of numerous 
* It may be mentioned here that no second case of a red-eyed Gammarus arising 
independently has occurred up to the present time (September, 1917), all the red-ey ed 
animals used in the experiments being descendants of the original stock. 
+ The term ‘‘ Albino” is here used to designate those animals in which the eye 
possesses no coloured retinal pigment, but in which the chalk-white extra-retinal pigment 
is present. For eyes in which the coloured retinal pigment and the chalk-white extra- 
retinal pigment are both absent we employ the term “colourless.” 
