ABNORMALITIES OF MAMMALIAN EMBRYO BEFORE IMPLANTATION. 65 



be decided; but in any event the specimen may be regarded as a true monster, the 

 earliest ever seen in a mammal. This and the other related blastodermic vesicles, 

 like those described in the previous paragraphs, were found lying unattached in the 

 cavity of a healthy uterus which was quite normal and which proved on microscopic 

 examination to be lined by a mucosa in every way similar to that of uteri containing 

 normal embryos. The Fallopian tubes presented no gross abnormalities; they were 

 not examined microscopically. 



In view of the positive evidence afforded by the few specimens gathered by 

 Huber and the writer, we are forced to the conclusion that the organism is liable to 

 pathological changes before its attachment to the uterus. Whether these are due 

 to faults inherent in the germ-cells, or to traumata which assail the ovum during 

 its passage from the ovary to the uterine mucosa (such, for example, as chemically 

 abnormal secretions of a seemingly normal uterus) our specimens of course do not 

 explain; they merely increase the difficulty of the problem by demonstrating the 

 inadequacy of the theory of faulty implantation to account for all developmental 

 aberrations. Most likely it will be proved in the end that the germ-cells and their 

 product are liable to the onset of abnormalities at all stages of their history; certainly 

 hints of such a possibility are given by two lines of investigation, as yet but little 

 applied to mammalian forms. The first of these comprises those experiments 

 already mentioned, which show that the eggs of fish and frogs are susceptible to 

 damage by all sorts of chemical and physical factors in their environment, at stages 

 of development so early as to be comparable with the segmenting mammalian 

 ovum during its passage through the tube and while in the uterus before implanta- 

 tion; the other line of approach is through the studies of Morgan and others, who 

 have discovered the occurrence in plants, insects, and even mammals, of inheritable 

 factors which, when brought into play by some unfavorable mating, cause such 

 deviation from the anatomical or physiological norm as to kill the individual at one 

 or another stage of its development. For instance, according to Cuenot, Castle, 

 and Little, it is impossible to breed mice which are homozygous for yellow coat- 

 color; it appears that the inheritance of this character through both parents is 

 invariably fatal to the embryo; and, indeed, the recent report of Kirkham hints 

 strongly that in this case the lethal factor may attack the embryo shortly before the 

 time of implantation, while it is still in the morula or vesicle stage. It seems not 

 impossible, therefore, that in future the application to mammals of both the 

 teratological and the genetic modes of experimentation may aid in solving the 

 complex but pressing questions arising from abnormalities of development of the 

 human organism. 



