Cytological studies on the spinning glands of Platyphylax etc. 399 



prepared some glands which had been active for shorter periods. With 

 these we were exact, waiting, in each instance, until the larva had 

 actually begun the construction of its case before timing it. All 

 larvae which were active longer than twenty-four hours had the new 

 case removed each day, thus, as far as possible, insuring continuous 

 activity. 



The glands which we used for our study by the first method we 

 have just described, were placed in the hardening fluid at very nearly 

 the same lime, so that, at most, only one or two minutes would elapse 

 before both were in the same bottle of fluid. Whenever we trans- 

 ferred the glands, either in toto or after sectioning, from one fluid 

 to another they were removed from and placed in the fluids with but 

 a few seconds intervening. We thus had glands taken from two 

 larvae, w^hich, excepting that one built new cases and the other did 

 not, had lived under similar conditions; these glands throughout the 

 process of hardening in toto and staining as sections, were always in 

 similar solutions for nearly equal lengths of time. 



Different solutions were used for fixation; Fleraming, hot water 

 followed by sublimate, two différent sublimate-acetic acid solutions, 

 and a saturated solution of sublimate in water. The stains we used 

 were iron-haematoxylin followed by Bordeaux red or Orange G, acid 

 fuchsin and metbylen-green, and Flemmiug's triple stain. Our best 

 results were obtained with Flemming's fixative followed by his triple 

 stain, and this combination w'as used more than any other. Both strong 

 Flemming and a dilution of it with one-half water were used. 



The spinning glands in Platyphylax, two in number, are about 

 one and one-half times the length of the body of the larva; they are 

 folded three times, as described by Gilson [4], and lie laterad and 

 slightly ventrad to the intestine. Each is divided into two portions, 

 an anterior, conducting portion, lying within the head, and a posterior, 

 secreting portion, which makes up by far the larger portion of the 

 gland. The two parts are slightly enlarged near the uniting ends and 

 there is a well marked constriction at the exact point of union, which 

 is at the posterior end of the head. The glandular portion is narrow- 

 est near either end and widest in the long median part. The two 



