September, iQoi] 



PSYCHE. 



247 



tome) of them. For this purpose the 

 skin of the thorax with attached buds 

 should be cut out, either in one piece 

 with all the buds, or in segmental pieces 

 with the buds of one segment, or in six 

 distinct pieces, each bud with a bit of 

 skin by itself. These pieces must be 

 properly hardened, cleared, infiltrated 

 with and imbedded in paraffine, sec- 

 tioned (cut into thin slices) by means of 



ment a longitudinal section (fig. 2, B) 

 i. e., one through skin and bud at right 

 angles to the long axis of the larva, it 

 may be seen that the bud is composed 

 of an invaginated part of the hypoderni 

 layer which has become folded, and in 

 which there has been a special increase 

 and growth of cells. The folding and 

 modification of this part of the hypoder- 

 mal cell layer is such that part of it. 



Kmt.t. 



h' m /. 



fig. 1. A, Larv<i of Siinulium, showing thoracic hisloblasts, as they show through the 

 skip; H, Larva of C/i/rdrt(j;««5. similarly showing thoracic histohlasts; C, Head and body" 

 wall of thoracic segments of larva of Hohriisia rubigittosti, showing histoljlasts ; h. /. r. his. 

 toblast of prothoracic respiratory tubes of pupa ; li. p. 1 . htstoblast of prothoracic leg, h, m, w_ 

 histoblast of wing, li. m, 1. histoblastmesothoracic leg, h. mt. b. histoblast of balancer, 

 h. mt. 1. histoblast nietathoracic leg. 



a microtome, and the sections fastened 

 to a glass slide in regular order, stained, 

 cleared, and finally mounted in Canada 

 balsam. For an account of the details 

 of histological technic with special refer- 

 ence to insects, see Comstock and Kel- 

 'ogg's Elements of Insect Anatomy, 

 1899, pp. 1 1 1-129. 



In any thoracic bud of Ilolonisia 

 which is about midway in its develop- 



called the peripodal membrane, is very 

 thin (compared with the rest of it) and 

 serves as a partially enveloping mem- 

 brane, and as the walls of a neck which 

 connects the thickened part of the his- 

 toblast with the hypoderm at the point 

 of invagination. It is the thickened 

 part of the invaginated hypoderm (the 

 inner part of the bud) which is to de- 

 velop into the wing, or leg, or balancer. 



