29 



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 -Hi/lodes 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, Avhatever 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 distri- 

 bution of matter capable of assuming a polar condition, and 

 free to move around a magnet, and the distribution of mat- 

 ter 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 



