The Development Theory : A Review. 115 



readily admit. In the third chapt3r are mentioned the causes 

 which, so far as is known, can and do develope variation. They 

 are summed up in the following sentence : — " Any change in the 

 circumstances, i.e., the sum total of the influences affecting any 

 organism, will be likely to work some alteration in that organism 

 or its descendants, or both." In confirmation of this position the 

 well-known instance of the brine-shrimp (Artemia — Branchipus) 

 is brought forward. A more obvious one, that of the Axolotl, we 

 extract, somewhat condensed. 



" The Mexican Axolotl is a tadpole-like creature of consider- 

 able size which lives in the water, breathes by gills, and is 

 reproduced from eggs. In its native country this creature is not 

 known to change its form. 



" Now in 1867 it was observed at the Jardin des Plantes, in 

 Paris, that some of these animals cast their skins after crawling 

 out of the water, and began a new existence in the shape of a 

 common Salamander (Ambly stoma). This astonishing change 

 from Axolotl to Salamander is accomplished in from fourteen to 

 sixteen days, and, it seems, may always be brought about in healthy 

 specimens by placing them in shallow water and gradually 

 diminishing the supply. The Salamanders so produced lay eggs 

 which hatch into tadpole-like larvae that soon grow into Sala- 

 manders." Several other cases of the same kind are given by the 

 authors for which we must refer the reader to the work itself. 



In reference to this part of the subject it is only fair to 

 remark that not a few cases can be quoted in which organisms 

 have refused, and do constantly refuse, to vary in spite of very 

 great changes of environment. Darwin called attention strongly 

 to this fact, and others have since done the same. Yet, allowing 

 full weight to the objection, it forms no insuperable barrier in the 

 path of the evolutionist. We know not what counteracting 

 influences may be at work to prevent the expected variation. 

 Even if with Darwin and others we attribute the refusal to vary 

 to a resistance on the part of the organism, yet that resistance 

 may be an outcome of past conditions, possibly a deep-seated 

 and long enduring habit. Strong and well established facts 

 proving variancy under varying conditions cannot be set aside by 

 negative facts. Similar difficulties are encountered by all great 

 generalization. The Copernican theory of the universe stumbled 





