64 Psyche [June 



adjoining tissues, which do not take the stain so readily. Balsam 

 mounts were prepared from legs excised above the bases of the 

 coxae, fixed in Gilson's mercuro-nitric mixture and stained in either 

 Ehrlich's acid haBmatoxylin (13 hours; then differentiated in 70 per 

 cent, alcohol which had been slightly acidulated with hydrochloric 

 acid, and dehydrated) or in alum-cochineal prepared according to 

 Guyer's formula- (36 hours; then washed 20 minutes in several 

 changes of water and dehydrated). Alum-cochineal was found to 

 produce more delicate differentiation. Ehrlich's haematoxylin also 

 gave good results, but its tendency to stain the material too deeply 

 makes it inferior to the alum-cochineal for preparations in toto. 



Anatomical Considerations. 



Except in size and in some other minor differences, the three 

 pairs of legs are apparently uniformly similar in their anatomical 

 characters. In the absence therefore of any important structural 

 modifications in any of the legs, no attempt is made in the present 

 discussion to treat each of the three pairs separately. 



The legs of aphids have two tarsal segments. In the case of 

 Myzus persicce the first segment (Plate IV, figures 1 and 3. C) is 

 nearly one-fourth the length of the second (Plate IV, figures 1 and 

 3. c). The former is subtriangular from the lateral aspect, and 

 is produced at the entoproximaP margin into two subconical pro- 

 jections, as follows : ( 1 ) A longer one, which is subconfluent with 

 the ental wall of the first tarsal segment (Plate IV, figures 3 and 

 5. H). This serves as the base for the insertion of a muscle which 

 by its analogy in function to certain vertebrate muscles will be 

 termed the extensor tarsia (2) A smaller projection which branches 

 from the former at the base and is directed entally with respect to 

 the median line of the insect's body at an angle of about 90 degrees 



- Guyer, M. F. 1917. Animal Micrology: 9. Chicago. 



» In this and the paragraplis which follow, sucli terms as ental, ectal, etc., 

 refer to tlie normal position of tlie leg with respect to the median line of the 

 insect's body. 



■• In vertebrates, muscles are usually "arranged in antagonistic groups, the 

 action of one being the opposite of its antagonist. Thus there are flexors to 

 bend a limb, extensors to straighten it. ..." Kingsley, J. S. 1917. Out- 

 lines of Comparative Anatomy of Vertebrates, second edition, revised: 134. 

 Philadelphia. 



