ORIGIN AND TRANSFORMATION OF ANIMALS. 669 
teristics of the group of which the new creature will form a 
part. 5 ’ 
We must refer the reader to M. Quatrefages’ agreeable 
volume for further details on this branch of the subject, and 
pass to the consideration of a few points in the development 
of the egg of the mammalia. Here our author tells us the 
heart soon makes its appearance, accompanied by arteries 
and veins, and soon after it the nervous system, the digestive 
tube appearing more late. This order of succession is 
directed by the method of nutrition, and it is inverted among 
the invertebrata, where the digestive apparatus precedes the 
circulatory. In watching the process of transformation, 
a every day, every hour, the scene changes, and this insta¬ 
bility effects essential as well as necessary parts, &c. 
Here cavities partition themselves into distinct chambers, 
or extend themselves into canals; and these, in their turn, 
are filled up and converted into ligaments; films are rolled 
up into tubes; isolated parts solder themselves together into 
continuous organs, or uniform masses divide themselves and 
form several organs. At the same time, relations and pro¬ 
portions change each instant. Parts which had been almost 
confounded, separate and become strangers; others, which 
had been separated, approach and contract intimate union. 
Organs with temporary functions, grow, increase rapidly, 
acquire an enormous size, and then become atrophied, and 
disappear. Others stop at a given moment, while ail grows 
around them. They retain their place, and will be found in 
the adult, where they have no other apparent part than to 
bear witness to a state of things which no longer exists/ 5 
Having got out of the egg and been born, the young 
mammal experiences transformations ,* the proportions of the 
several parts altering at each stage, that of puberty being 
highly interesting and important. MM. Andral and Ga- 
varret state that at an early age boys and girls respire with 
equal vigour. Before puberty M. Quatrefages calls them 
neither males nor females, but neuters. “ But as soon, 55 he 
says, (< as the sexes are characterised, the respiration of the 
young man exhibits a redoubled and rapidly augmenting 
activity, wdiile in the young girl and young woman this 
function remains stationary. About the age of thirty the 
former burns about 170 or 186 grains of carbon in an hour. 
Subsequently, when the progress of age, and its accom- 
* M. Quatrefages entitles the chapter from which these remarks are taken 
“ Transformations des Mammiferes hors de l’oeuf.” Thus he does not fol¬ 
low the nomenclature which he recommends, and according to which these 
changes would be metamorphoses. 
