467 



for from thirty minutes to six hours according to the size of the larvae. 

 Specimens were put into the first solution alive and were then quickly 

 withdrawn, cut in several places, and put into the weaker solution. 

 The material was dehydrated in the usual manner, cleared in a mix- 

 ture of Cedar oil and Xylol, and imbedded in paraffin. Sections were 

 cut 62/3 H^- ^^^ 10," iïi thickness, and stained with Heidenhain s Iron 

 Haematoxylin , and Mayer's Haemalum, and double stained with 

 Orange G., or Zwaardemaker's Safranin. 



Material killed in Perenyi's fluid, several Picric Acid mixtures, 

 hot water, Hermann, Fleming (strong formula) and vom Rath, 

 was also studied. The three latter gave results which were good, but 

 not as uniform as the sublimate-acetic acid mixtures. I found Perenyi 

 and the Picric compounds entirely unreliable, whereas hot water gave 

 only a fair preservation. 



The existence of a fluid between fhe old cuticula and the new at 

 ecdysis was first observed by Newport. This discovery has been con- 

 firmed many times by others, but Gonin (1S94) was the firstto demon- 

 strate its presence by modern histological methods. According to the 

 observations of this author and of Professor Bugnion (Packard, 

 1898), a liquid was found which nearly or quite covered the surface of 

 the larva [Pieris brassicae) at ecdysis. At the same time, the authors 

 noticed certain large cells, lying as Bugnion states, in the region be- 

 tween the head and the prothoracic segments. These cells were seen to 

 be extruding between the two layers of cuticula a substance which 

 ■was coagulated by the reagents, but they did not seem to the authors 

 to be true glands like the unicellular glands of other forms. The 

 authors further state that if these cells do function as organs secretine 

 this exuvial fluid, they ought to be found scattered all over the body 

 instead of restricted to a small area, and this seemed to them a good 

 reason for thinking that these cells do not secrete all of this fluid or 

 perhaps any of it, but rather that it is secreted by the hypodermis in 

 every part of the body. 



In the form which I have studied, there is a distinct, and often a 

 large coagulum in sections made of larvae that are undergoing ecdysis. 

 Not only at pupation, as has been observed by Newport, Gonin, 

 Bugnion and others, but at every moult this fluid is formed in greater 

 or less abundance, separating the old and new cuticulas, but it is most 

 copious at the moult which the animal undergoes when the larva 

 becomes a pupa. 



In L. decem-Uneata there are found at ecdysis in, or just below 

 the hypodermis, large, highly vacuolated cells with deeply staining 

 nuclei. These cells often send blunt processes through the hypodermis 



31* 



