In our last number we presented our readers with a general abstract of the first part of this valuable work. The second part refers to animals of the _cold blood_ order, including _fish_ and _reptiles_. The _larvæ_ of the latter underwent some comparative experiments detailed in the first chapter, because they partake of the nature both of _fish_ and _reptiles_, as to their _respiratory function_; the imperfection of their intermediate state and developement of organization not interfering with the objects in view, and the double mode of aërification being exercised unequally. The _skin_ of these young animals furnishes them with the means of producing the requisite changes in the blood by _absorption_, as in the adult, while it lives in water; and the cutaneous respiration goes on through this medium at a temperature which the subsequent more perfect animal is unable to endure. The object entertained is the influence of physical agents upon the changes which these animals pass through in their form and structure. An important condition of their advancement to maturity seems to be, that the nutriment suspended in the water should be in very small and limited proportions. Temperature also influences their constitutional changes. Sometimes the _larvæ_ pass through the winter in their primitive state; a fact not generally known. Some _tadpoles_ were confined within wooden boxes submersed in the river Seine, in which holes were perforated to allow the stream to pass through, without the possibility of the animals rising to the surface of the water, and thus to inhale air. Others were placed in a large vessel of Seine water renewed at intervals, with power to rise above the surface. Ten in twelve of the first box underwent no transformation, the others having gone partially through their change. But [p297] those of the large vessel, and not submersed in the river, passed through their changes of form without the least appearance of the phenomenon being retarded. The running waters of the Seine probably contained nutritious matter, which the water periodically renewed was more deficient in. Under circumstances of moderate nourishment and temperature, the tadpoles under water did not complete their changes but in a very partial and protracted manner, while the greater portion made no change. The great difference in the circumstances of the experiments seems to have been the access to the air of those which went through their transformations as usual. Exclusion from light made no difference in the results, and these were solely influenced by occasional renewal of air from pulmonary respiration.