298 [December, 



ethology aud morphology in a series of generations ? Does a difference 

 in habit extending through a series of generations involve (or induce, 

 or become correlative with) a difference in structure?* 



There are some who will assert the contrary, and say that it is 

 just as probable that a morphological differentiation precedes an etho- 

 logical one. And no doubt the two differentiations in a series of 

 generations re-act in such a way that each intensifies the other, as 

 may be read in the first edition of Herbert Spencer's Principles of 

 Biology in the chapter relative to Structure and Function. 



There is thus not much difficulty in understanding that the mor- 

 phological and ethological distinctions in the two wasps are correlative ; 

 and in fact only different aspects of a single differentiation. 



But, it will be asked, how comes it that these differentiations have 

 not been obliterated by crossing ? One would suppose that the two 

 forms when still very imperfectly differentiated would, if they lived 

 together, interbreed and so obliterate the nascent distinctions. 



This is evidently the view that has induced Mr. Saunders to speak 

 of austriaca as an inquiline. Here I differ a little from him. An 

 inquiline is a guest that is not really of the family. 



I believe it will be found that ethological segregation is a highly 

 important factor in morphological differentiation. 



At the present time the difference in the offspring of the group 

 of individuals having two kinds of females and the group having un- 

 differentiated females is accompanied by a difference in habits (workers 

 in one case, no workers in the other). And as "birds of a feather 

 flock together " in the human colony, so I have no doubt they did in 

 the primitive wasp colony. Aud the segregation thus induced would 

 be sufficient to prevent complete interbreeding. It is probable that 

 even at the present time there is occasional interbreeding, and I 

 expect that observation will show that there is a good deal of social 

 segregation in the nests. 



To sum up. The old common stock from which both V. rufa and 

 austriaca are derived has differentiated into two nearly, or quite, dis- 

 tinct forms which have never ceased to live together. They have 

 been prevented from the results of thorough intercrossing by etho- 

 logical segregation due to the differences in instinct and physiology, 

 arising from the differences in their industrial and reproductive powers. 

 Probably both have changed morphologically during the evolution, 

 but the present V. austriaca is the more nearly i-epresentative of the 

 original stock. 



* A diiference in colour is of course a difference in structure. 



