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 

 branchiae 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 larvae 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 Foetus " (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 



