INHERITANCE OF EYE-COLOUR IN GAMMARUS. on 
The records of the individual families are very interesting. In K 
family, in which females preponderate, breeding commenced October 25, 
1914, the first thousand was reached on April 20, 1915: 63 broods 
hatched out numbering in all 1007 young, of which 756 were Black and 
251 were Red, exact proportions. In the second thousand there were 59 
broods hatched containing 1003 young, 767 Black as against 236 Red, 
the Black therefore in excess. 23 more broods were laid with 431 young, 
336 Black and 95 Red. As will be seen, the proportion of Black is again 
higher. The last male died on September 21, 1915, on which date the 
records were perforce brought to a conclusion. 
These figures prove conclusively that in the F, generation the pro- 
portions are 3 black-eyed to 1 red-eyed. The next step was the testing 
the black-eyed F, to get the proportion of Pure Black to Hybrid Black, 
but the results of this work are not exact and naturally cannot be. It is 
easy enough to separate the colours, black from red, immediately on 
hatching, but impossible to determine the question of the constitution of 
the black-eyed until they breed. Owing to various causes a high rate of 
mortality has to be allowed for, and the results therefore can only be 
given on the survivors. 
The animals undergo many ecdyses, the young every few days, the 
adults at longer intervals, the males again at much longer intervals than 
the females. The moulting period is always critical even to the strong 
ones. It is absolutely fatal to the weakly ones in a brood, the others 
attacking them in their feeble condition and devouring them. With the 
adults the mortality is higher among the females. The reason is that the 
male carrying the female for some days prior to the extrusion of a brood, 
and assisting it through the moult which immediately precedes the de- 
position of a fresh brood, very frequently ends by eating it directly after. 
A great many females have been lost in this way in the course of the work. 
But the principal cause of the high death rate is the development of 
injurious bacteria in the bowls. At first it was thought that the bacteria 
had been introduced with the rotting leaves given as food, and many 
methods of sterilising the leaves were tried. After a while it was noticed 
that all the broods set out on a certain date had perished, and on com- 
paring this result with a similar one in Mr. Crawshay’s experiments, he 
discovered that the same sea-water had been used in all, and that this 
water was infected, although taken as far out as the Eddystone for the 
sake of avoiding shore contamination. 
Several kinds of bacteria have been observed, some fatal within a day 
or two, some after several weeks, and others which, except for retarding 
development, do not injure the animal. One of this last-mentioned kind 
turns the water a milky colour, and forms dense slimy masses all round 
NEW SERIES.—VOL. XI. NO. 1. MARCH, 1916. C 
