iv ANTS 143 



determined by those " Anlagen " or rudiments that Weismann 

 and his school consider to be all important in determining the 

 nature or form of the individual, for if this were the case, how 

 can it be, he asked, that one egg may produce either a worker, 

 nurse, soldier or female ant ? To this Wasmann (who continued 

 the discussion) replied by postulating the existence of double, triple 

 or numerous rudiments in each egg, the treatment the egg receives 

 merely determining which of these rudiments shall undergo de- 

 velopment. 1 Forel seems to have adopted this explanation as being 

 the most simple. The probability of Weismann's hypothesis being 

 correct is much diminished by the fact that the limit between the 

 castes is by no means absolute. In many species intermediate forms 

 are common, and even in those in which the castes are believed to 

 be quite distinct, intermediate forms occur as very rare excep- 

 tions. 2 Emery accounts 3 for the polymorphism, without the 

 assistance of the Weismannian hypothetical compound rudiments, 

 by another set of assumptions ; viz. that the phenomenon has 

 been gradually acquired by numerous species, and that we see it 

 in various stages of development ; also that variation in nutrition 

 does not affect all the parts of the body equally, but may be 

 such as to carry on the development of certain portions of the 

 organisation while that of other parts is arrested. Speaking 

 broadly we may accept this view as consistent with what we 

 know to be the case in other Insects, and with the phenomena of 

 post-embryonic development in the class. But it must be ad- 

 mitted that our knowledge is at present quite inadequate to 

 justify the formulation of any final conclusions. 



The geological record of Formicidae is not quite what we 

 should have expected. They are amongst the earliest Hymen- 

 optera ; remains referred to the family have been found in the 

 Lias of Switzerland and in the English Purbecks. In Tertiary 

 times Formicidae appear to have been about the most abundant 

 of all Insects. At Florissant they occur in thousands and form 

 in individuals about one-fourth of all the Insects found there. 

 They have also been met with numerously in the European 

 Tertiaries, and Mayr studied no less than 1500 specimens found 



1 Biol. Ccntralbl. xv. 1895, p. 640. 



2 Prof. Forel has favoured the writer by informing him of several cases of these 

 rare intermediate forms he has himself detected. 



3 Biol. Centralbl. xiv. 1894, p. 53. 



