JEFFRIES WYMAN. 393 
worked out all the details of the development of the Suri- 
nam toads in the skin of the back of their mother, and would 
equally have noted the morphological significance of the 
branchie and tail, that are never to know anything of the 
element they are adapted for; but Dr. Wyman remarks upon 
the development of the limbs independently of the vertebral 
axis, as showing that whatever view be taken of their ho- 
mology, they are something superadded to it, and not evolved 
from it; he notes how the whole yelk mass is moulded into 
a spiral intestine; and that the embryo at the end of incu- 
bation forms a larger and heavier mass than existed in the 
egg when it commenced, — showing that there was an absorp- 
tion of material furnished by the dermal sac of the mother, 
— ‘a solitary instance among Batrachians, if not among rep- 
tiles generally, in which the embryo is nourished at the ex- 
pense of materials derived from the parent.” From this he 
is led (in the last paper above mentioned) to infer the prob- 
ability that the developed larve of Hylodes lineatus — car- 
ried about inland upon the back of their mother, and destitute 
of limbs adapted to terrestrial locomotion — may depend 
upon a secretion from the body for needful sustenance, — an 
interesting and rudimentary foreshadowing of mammalian 
life, of which he discerned the bearings. 
His “ Description of a Double Fetus” (in the “ Boston 
Medical and Surgical Journal,” March, 1866) gives him the 
opportunity of briefly recording some of the results of his 
studies of the development of double monsters, and to bring 
out his view, that “the force, whatever it be, which regulates 
the symmetrical distribution of matter in a normal or abnor- 
mal embryo, has its analogy, if anywhere, in those known 
as polar forces;” that, “studying the subject in the most 
general manner, there are striking resemblances between the 
distribution of matter capable of assuming a polar condition, 
and free to move around a magnet, and the distribution of 
matter around the nervous axis of an embryo.” That this is 
not one of those vague conceptions by which many speculators 
set about to explain that of which they know little by means 
of that of which they know less, but that he had striking 
