NATURAI. HISTORY OF AMERICAN LOBSTER. 
167 
In the lobster the conditions of development aie intermediate between such 
extremes, but in weighing them the structure and habits of the animals at every stage, 
the environment, and their adjustment to it must be considered. The whole period of 
development is long, followed by a long period of adolescence, but the relative duration 
of the swimming life, which is about 3 weeks, is shorter than in the starfish or in 
Palinurus (see p. 160). This is a fortunate cireumstance in view of the possibilities of 
artificial propagation, as will be later seen. 
While the abbreviation of the metamorphosis is attended by an accumulation of 
yolk in the egg, it is impossible to explain either how this has been effected or why in 
any case such a course should have been followed to secure greater harmony or fitness 
to the environment. 
In fresh -water forms and in deep-sea species the shortening of the metamorphosis 
may be more uniform and the advantage derived more apparent. In all cases, however, 
it is a question of the survival of the young, but no one can say why in Palinurus the 
problem has been solved by increasing the number of individual chances and in the lob- 
ster by lengthening the period of fosterage and reducing that of the larva. In any case 
the tax on the parent, when no parental instinct is involved, is essentially the same, 
though the items are changed, since the total amount of food yolk manufactured in the 
ovaries of a crab, which lays millions of eggs, is probably not relatively greater than that 
produeed in the organs of the lobster, whose eggs are counted only by tens of thousands. 
The greater the size of the egg, however, the longer is the tax issue upon the energy of 
the young deferred and the greater the reduction of its rate. 
The adjustment represented by either extreme is certainly advantageous in the 
long run, but probably neither is the best under all circumstances. 
FAMILY LIFE IN CRAYFISH. 
The crayfishes, which are now all inhabitants of fresh water or burrowers in soil 
where moisture is available, are undoubtedly descended from marine lobster-like 
ancestors, and, as we have seen, for reasons not fully understood have undergone a 
still greater reduction in larval development. They have, further, acquired an inter- 
esting family life, which was noticed by Rosel von Rosenhof over one hundred and fifty 
years ago. An adequate account of this relation has finally been given by Andrews,® 
and in concluding this chapter we shall give a resume of one phase of it, based upon his 
work. 
Metamorphosis has been curtailed to such an extent in Astacus and Cambarus that 
they are hatched in a form which suggests the fourth stage of the lobster. In reality 
the young crayfish presents a curious compound of embryonic, larval, and adult char- 
acters. The peculiar family relation which serves to tide the young over a helpless 
period of infancy to complete independence endures, according to Andrews, for about 
a fortnight, or until after the second molt in Astacus and after the third in Cambarus. 
a Andrews, E. A. The young of the crayfishes Astacus and Cambarus. Smithsonian Contributions to Knowledge, vol. 
XXXV, no. 17, 18, p. 1-80 ; pi. i-x. Washington, 1907. 
