FISHERY BULLETIN: VOL. 70, NO. 1 



divided by two. The resulting figure was used 

 as an index of development only and was not 

 meant to represent the actual increase or growth 

 of the eye. Samples of 15 to 20 eggs were re- 

 moved from the periphery of an egg mass when- 

 ever a measurement was desired (usually once 

 a week) . From these samples five eggs were se- 

 lected randomly, and one eye of each embryo 

 measured. A mean of these five measurements 

 was used as a working figure or index. Eggs 

 were taken from the peripheral layer of the mass 

 as these are the furthest advanced in develop- 

 ment and are the first to hatch. Variation in 

 the eye measurements of eggs from this layer 

 ranges from zero to o^C When the eyes first 

 appear and are large enough to measure, they 

 are but thin crescents, darkly pigmented and 

 surrounded by a halo of lighter material. The 

 dark crescents only were measured. The eyes 

 are very distinct for most of the developmental 

 period and are easily measured, the crescents 

 gradually becoming tear-drop in shape. The in- 

 dex of the eye is about 70/x when it is first mea- 

 surable; the index is about 560/i at hatching. 

 All eyes were measured after the eggs had been 

 preserved in a 5/f solution of Formalin in sea- 

 water. Preservation in Formalin caused sig- 

 nificant swelling in the eggs themselves but had 

 no determinable effect on the size of the eyes. 



year, water temperatures were no higher than 

 6° C. Embryonic development during this pe- 

 riod ceased in some of the egg masses and was 

 barely discernible in others, at least by the 

 method of eye index measurement. Squires 

 (1970) , using the amount of yolk material in the 

 eggs as a criterion, reported a standstill in devel- 

 opment during the winter in embryos of New- 

 foundland lobsters. 



tfi 600 



I 500 



y 400 



Z 500 



S 200 



o 100 



Eye Pigment Stofis 



600 

 500 

 400 



xa 



200 

 100 

 



JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG 



Figure 1. — Trends of development of the embryos of 

 five female lobsters held in water of seasonal temperature 

 at the Boothbay Harbor Laboratory and the temperature 

 cycle during the period. The lines showing develop- 

 mental trends are derived from plots of periodic measure- 

 ments of the embryos' eye indices. The lines are num- 

 bered in accordance with the age of the egg mass; the 

 lower the number, the older the egg mass. 



RESULTS AND DISCUSSION 



TRENDS OF EMBRYONIC DEVELOPMENT 



IN WATER OF 



SEASONAL TEMPERATURES 



The developmental patterns, from onset of eye 

 pigment to hatching, of the embryos of the five 

 females held at seasonal temperatures are shown 

 in Figure 1, as is the cycle of water temperature 

 for the same period. The trends of embryonic 

 development were plotted by using periodic (usu- 

 ally weekly) measurements of the eye index of 

 each egg mass. These five lobsters had extruded 

 their eggs in the laboratory tanks so the age of 

 each egg mass was known. From the latter part 

 of November to the first of May of the following 



DIFFERENTIAL RATES OF DEVELOPMENT 



The developmental rates of lobster embryos 

 appear to be governed not only by their thermal 

 environment, but by the age or extent of de- 

 velopment at which they are subjected to that 

 environment. During the experiments I con- 

 ducted the older or more advanced embryos de- 

 veloped at slower rates than those less advanced, 

 though all were maintained in the same tank. 

 The oldest egg mass of the five females held under 

 seasonal conditions was extruded 7 weeks before 

 the youngest, but the total time for development 

 of the younger egg mass was 414 weeks less than 

 the older; the younger embryos had developed 

 considerably faster. Measurements of the eye 

 index of embryos in all five egg masses were 

 made for the first time on November 7. In Fig- 



96 



