460 WM. E. KELLICOTT 



varies with same internal or fluctuating condition of the egg and 

 also with its stage of development. 



We should also point out here that Lillie and Knowlton ('97) 

 found that eggs of the frog (Rana virescens) at 2-3° C. always 

 developed abnormally, if at all, the abnormalities usually appear- 

 ing in the region of the blastopore. 



In his classic ''Study of the Causes Underlying the Origin of 

 Hum£n Monsters," Mall ('08) included an extensive survey of 

 the more important results in the whole field of experimental 

 teratology, particularly among the vertebrates. He concludes 

 that even in such dissimilar instances of teratogeny as those in 

 the toad resulting from fertilization with X-rayed spermatozoa 

 (Bardeen, '07), those in the Teleost following chemical treat- 

 ment during cleavage (Loeb, '93, Stockard, '06, '07) and the 

 human instances described by himself, ''although the methods 

 employed are very different, the principle involved and the 

 results obtained are much the same" (p. 24). And, "In general 

 the methods employed by experimental teratologists is to sub- 

 ject the eggs to various insults which affect the nutrition and 

 impair the growth of the embryo" (p. 52). "A monster is due to 

 the influence of external substances which retard the growth of 

 the embryo, usually one portion more than the other" (p. 36). 

 In brief Mall's conclusion regarding the causes of human mon- 

 sters is that "faulty implantation of the ovum, which naturally 

 affects the growth of the embryo" (p. 25), by interfering with 

 the normal nutritional relations leads to monstrous develop- 

 ment ; ' '.that certain parts of the embryo are more susceptible to 

 insults than others" (p. 32), and consequently it is these that 

 are affected first (p. 16), though subsequently the faulty im- 

 plantation must be remedied so that the emibryo may continue 

 to grow (p. 25). "But in order to produce a finished monster 

 the nutrition must not be impaired too much" (p. 31). Many 

 other quotations from the same work might be added to show 

 that the words nutrition and growth are used with their custom- 

 ary significance, implying only the supply of materials and en- 

 ergy necessary for the usual processes of extension of at least 

 partially differentir.ted' stiuctures or anlagen. Disturbances of 



