Gray.] 116 [October 7, 



excellent opportunities, would have worked out all the de- 

 tails of the development of the Surinam toads in the skin of 

 the back of their motherland would equally have noted the 

 morphological significance of the branchiae and tail, that 

 are never to know any thing 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 homology, they are some- 

 thing 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 incubation forms a larger 

 and heavier mass than existed in the egg when it com- 

 menced, — showing that there was an absorption of material 

 furnished by the dermal sac of the mother, — " a solitary in- 

 stance among Batrachians, if not among Reptiles generally, 

 in which the embryo is nourished at the expense of materials 

 derived from the parent." From this he is led (in the later 

 paper above mentioned), to infer the probability that the 

 developed larvae of Hylodes lineatus, — carried about inland 

 upon the back of their mother, and destitute of limbs 

 adapted to terrestrial locomotion, — may depend upon a se- 

 cretion 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 



; 



