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THE A M ERIC A N NA TURALIST [Vol XLI 



In ApanieJcs ghmcraius, owing to the thinness of the glandular 

 walls, it was inipossihle to secure tangential sections which would 

 give surface views of the nuclei. As the nuclei do not stain deeply 

 at this stage, they ai-e rather difficult to differentiate, although we 

 secured faiiiy good toults by staining with Grenadier's borax 

 carmine. :i> .liowii in figure 34. 



The (yt()i)la><ni is dense, granular, and vacuolated, especially 

 during the latter part of the larval life when the glands are at the 

 height of their activity (PI. 1, figs. 10 and 12). Through the 

 cytoplasm run trabeculae, extending in many cases from the exter- 

 nal border to the inner margin of the cell. These trabeculae 

 appear as fine radiating lines, but later, with the thiiming of the 

 glandular walls, they disappear. 



Gilson, '90, performed some interesting experiments in order 

 to determine the method of secretion. He ligated the entire liv- 

 ing larvae, disposing the ligatures in two pairs, the two threads of 

 each pair being close together. He then divided the larva into 

 three sections by cutting between each pair of ligatures. Treat- 

 ing the cut surfaces with mercuric chloride and collodion he secured 

 living isolated portions of the c-aterpillar, in each of which the 

 silk glands, es])ecially near the ligatures, continued to secrete. 

 1.1 .u<-h isohited portions hefouud vacuoles present in thecvtoplasm 

 un.l even in the iniel.'i of the >ilk ulan.l>. 'VUv>v vacuoh'. he e.,n- 

 Mdered ,he .ilk ^.'eretion. lie did not .Ueeeed in e.tal.lishing 

 whether they h.y Ix'twe.^n the radiating iral.ecnhi,^ or not. In 

 the case^ of Apanfrlrs ,,l.>mrratu.^ the condition which ( dlson sought 



the secrcte<l product is used till at the time of emergence from the 

 host. Xmnerotis vacuoles are present in the cytoplasm, becom- 

 ing most abundant dining the time of the greatest glandular activ- 

 ity. The contents of these vacuoles remain unstained bv anv of 



st;)in. «l a^ i^ iioted hilcr. Wlu'thcr the presence of tlie.e vaeiioh's 



sists of but two^ecn-ting tulx'.. lying one on .'aeh ^i.h' ..f the ali- 

 mentary canal (I'l. 1, iig. 1 i. Each is formeil by tlie union of the 



