1920] 



Patch: Aphids and Coccids 



163 



formation which has to do with the loss of such organs as char- 

 acterized them as insects in the first instar, rather than in the 

 acquisition and development of the structures of an adult 

 hexapod. This metamorphosis by reduction, associated with 

 the complete absence of wing development in the female is cor- 

 related with the sedentary habit of this family and is in line 



VI. COCCIDS. Generalized Outline.* 



Male 



1st Instar 

 active 



I 

 2nd Instar 



Xylococcinae active. 



Monophlcebin« active. ' 



Er.i9coccinae active to near end of period. 



Diaspinae quiescent. 



3rd Instar 



Xylococcinae quiescent. 

 Monophloebinae active. 

 Eriococcinse quiescent. 

 Diaspinae quiescent. 



4th Instar 



Xylococcinae quiescent. 

 Monophloebinae quiescent. 

 Eriococcinae quiescent. 

 Diaspinae quiescent. 



5th Instar 



Xylococcinae quiescent. 

 Monophlebinae adult. 

 Eriococcinse adult. 

 Diaspinae adult. 



6th Instar 



Xylococcinae adult. 



Female 



1st Instar 

 active 



I 

 2nd Instar 



active or fixed. 



3rd Instar 



active or fixed. 

 Diaspinae adult. 



4th Instar 



Xylococcus fixed. 

 Monophloebinae adult. 

 Eriococcinae adult. 



5th Instar 



Xylococcus adult. 



* This outline is given by courtesy of Dr. A. D. MacGillivray, to whom thanks 

 are also due for a critical reading of the Coccid part of the present paper and for 

 certain suggestions that have been incorporated. 



with the atrophy of class structures in parasitic animals. But 

 the suppression of generalized characters does not inhibit the 

 appearance of special structures of a high degree of develop- 

 ment, as is beautifully illustrated by the wax glands, marvelous 

 in form and variety, to be found in the coccids; a concentration 

 of structural effort directed toward the secretion of a waxy 

 protection for these sedentary creatures and their eggs. 



