SI 4 The Unit J/ of the Organism 



"keys" for tlic identification of the species are frequently 

 given for tlie larvae as well as for the adults. I have seen 

 no work on the subject in wliich the eggs are treated in this 

 diagnostic way, but in the ""Report of the Xezv Jersey State 

 Agrieultural Expei'iment Station upon the Mosquitoes oc- 

 curring within the State, their Habits, Life History, etc.''' 

 by Dr. John B. Smith, we read, "Dr. Dupree tells me that 

 he has found good characters in both eggs and larva? ; but 

 that they are observable only with the compound micro- 

 scope." ^'^ 



Tlie truth arrived at in other connections from more 

 theoretical considerations, that the fertilized egg from which 

 an individual animal develops is that individual in the one- 

 cell stage of its life, comes most vividly to view" in just these 

 purely practical studies. Thus in one of the many reports 

 by Fr. Heincke on the food fishes of the North Sea, the 

 author says : "The first condition for a right understanding 

 of the habits and habitats of the food-fishes of the sea, and 

 in general, of the production of the sea as regards useful 

 fishes, is an exact knowledge of the occurrence and dis- 

 tribution of tlicse food-fishes at all the various stages of 

 their life, from the egg on to the adult mature form.'" ^^ 



Facts of the sort here set forth have seemed to most biol- 

 ogists too trivial to deserve consideration in theoretical 

 discussions, and so far as they have been studied, this has 

 been done for the most part either incidentally, or, as in 

 the cases here adverted to, for practical ends. 



(/;) Grounds for Belieiing Minute Observable Specific 

 Differences Between Germ-Cells Important 



No matter how minute and superficial may be the at- 

 tributes which distinguish the egg-cell stages of species, 

 if these attributes are indubitable and constant they differen- 

 tiate the species iri that stage of the individuals' lives, and 



