18 MEMOIR II. 



moment they assmiie an elongated form; their heads bcini; 

 towards the breast of the mother, with the curvature of 

 the tail part suited to that of the outline of the pouch, the 

 convexity being at the same time invariably on the belly 

 side, fig. 1 1, which is the more singular, since the curvature 

 of the perfect animal, and of other embryo Crustacea is as 

 invariably in a quite opposite direction ; after this manner, 

 they lie closely compacted together, and present a perfectly 

 symmetrical arrangement, easily observed from the trans- 

 luccncy of the valves of the pouch, and the large size and 

 blackness of their eyes. 



This curious and extraordinary piece of economy can 

 hardly fail to be regarded by the Physiologist as equally 

 interesting with that of the Opossums, and other Mar- 

 supial Quadrupeds, and of a much more unaccountable 

 nature; for in these last, although theobject of the Creator 

 is not obvious, yet we can understand the manner in which 

 it is carried into effect, the young being excluded from the 

 uterus when they have scarcely attained a fourth part of 

 the growth of the embryos of other animals — naked, help- 

 less and blind, they are received into the abdominal pouch 

 of the mother, and by some wonderful instinct, or by the 

 mother's agency, attached each to one of the teats which 

 are situated within it, from whence, when sufficiently 

 grown, they make occasional sallies, until able entirely to 

 provide for themselves ; in the Opossum Shrimp on the 

 contrary, we comprehend the object, but are completely 

 at a loss to account for the manner in which it is brought 

 about, for these animals have nothing analogous to teats, 

 the embryos have no visible attachment to the mother, 

 appear to be in no capacity to take food, nor to carry on 

 the respiratory function. It is nevertheless probable, that 

 the secretion in which they are immersed, constitutes the 

 source of their nutrition, whether taken in by suction or 

 by absorption ; yet if we admit this, what are we to think 

 of the function of respiration thought to be equally neccs- 



