304 NATURAL SCIENCE. April, 



In regard to the scientific utility of these researches in experi- 

 mental embryology, it may be noted that a number of general results 

 are very clear, (i.) There is a great deal of life in an egg. Three- 

 quarters, a half, a quarter will in favourable conditions form a com- 

 plete larva. (2.) There is no little plasticity in the germ ; the 

 segmentation may be profoundly altered, the shape of the young 

 embryo may be greatly changed, and a new type of larva may be 

 produced. Yet the inherited characteristics are strong, for the ex- 

 periments show a marked tendency in the germ to reach a normal 

 result even by an abnormal path. (3.) To analyse out a definite 

 factor — say osmotic pressure — in teratogeny is beyond dispute 

 useful, for it may help us not only to understand malformations 

 occurring among higher vertebrates, but also to get nearer an under- 

 standing of the conditions of normal development. (4.) As every- 

 one knows, there are few facts, or, some would say, no facts, which 

 can at present be cited with confidence as direct evidence of the 

 transmission of environmentally-produced variations ; and Weis- 

 mann's case against the possibility of acquired somatic variations 

 specifically affecting the reproductive cells is strong enough to lead 

 many to depreciate, except in the case of simple Protozoa and 

 Protophyta, the direct influence of the environment as a factor in the 

 origin of transmissible variations. Be that as it may. How many 

 ova are there which float in the sea and in other media ; these are 

 now, as similar ova have been in the past, exposed to the influence of 

 very complex physical and chemical conditions ; that their living 

 stuff may be greatly affected the results of experimental embryology 

 show ; it is likely that the same is true in Nature's great laboratory ; 

 and the results, being germinal, may be transmissible. We need not 

 be in haste to exclude the direct influence of the environment from 

 among the primary factors of evolution. 



One practical application occurs to me. Many abnormalities in 

 the segmentation of the ova of littoral animals, e.g., Gasteropods, 

 have been noticed by various zoologists. The other day, in examining 

 the ribbons of eggs which Doris lays in such abundance on the 

 low-tide rocks, I noticed the great frequency of twins and triplets. 

 In some cases they seemed to preponderate. Is it not likely that an 

 explanation may be found in the fact that the ribbons are battered to 

 and fro by the surge ? What is done in the laboratory may also occur 

 on the shore. The shaking may separate the segmentation-cells and 

 mechanically produce twins. This is, of course, nothing more than a 

 suggestion, in default of the obviously necessary experimental 

 verification, but I find an interesting confirmation in C. Chun's 

 observation that twin Ctenophora were most abundant after stormy 

 days. 



