DIMORPHISM IN CHAITOPHOEUS ACEEIS. 127 



point of view. Whatever may be the modern outcome 

 of the question how variation is caused (for surely 

 more is wanted than the facts, if true, that variation 

 on a large scale is going on around us), and whether 

 certain assigned causes are sufficient to explain the 

 existence of the multitudinous entities regarded by 

 classifiers as species, there can be no doubt that scien- 

 tific investigation has received a powerful impetus 

 from the new theoretical bias, and that already a rich 

 harvest is being reaped under its influence, much of 

 which is gathered in from channels aside from the 

 main issue. 



Thus it is that some will look with much interest 

 on anomalies of development, and possibly in these 

 foresee points of departure leading to other and per- 

 haps more specialised races. Every phenomenon that 

 seems to lend a bearing, positive or negative, on the 

 question will be given a welcome as affording addi- 

 tional materials for forming an opinion on the subject, 

 which, if ever settled, will alone be so through a basis 

 of sound experiment and observation. 



The young of Chaitophorus aceris, it has been before 

 stated, occurs under two very distinct forms. One 

 of these is normal in its metamorphosis, and requires 

 here no special notice, the other is simultaneously pro- 

 duced, but after a slight growth continues for months 

 in a quasi-arrested condition, and finally dies without 

 having developed in itself any reproductive organs. 



In the ' Transactions of the Microscopic Society ' 

 of 1852, Mr. I. Thornton described under the name of 

 PhyUophorus testudinatus a Hemipterous insect feeding 

 on the common maple, and he justly considered this 

 insect as a larva of some indeterminate Aphis. 



Mr. Lane Clark also observed the same insect in the 

 year 1858, and placed it between the families Aiolii- 

 diclcB and Goccidoi, under the name of Chelymorjdia 

 testudo. 



In the year 1862 Vander Hoeven, of Leyden, pub- 

 lished another memoir on the same insect, and gave it 



