56 C. T. VORHIES. 



spinning-gland nuclei and the fact, as shown by Korschelt's work, 

 that changes in the formulae of certain stains may give conflicting 

 results, it seems very desirable that evidence of a somewhat dif- 

 ferent kind be obtained, if possible. It was with the object of 

 ontogenetic evidence in view that the present work was begun. 



It may be remarked at the outset that it was not anticipated 

 that the task would prove quite so easy of accomplishment as it 

 has, since it was supposed that the later embryonic stages would 

 require investigation. This proved not to be the case, however, 

 the earliest stages necessary to solve the problem being the young 

 larvae as they emerged from the egg. 



MetJwds. -^ It was found that the spinning-glands must be dis- 

 sected or teased out before fixation to secure the best results, 

 since even the youngest larvae are not penetrated readily by 

 the fluids. Decapitation gives quite good results, as some parts 

 of the glands will then usually protrude from the cut end of the 

 body. The most satisfactory method found for the smallest larvae 

 was to plunge them alive into the fixative, then turning the ven- 

 tral side up, and holding the posterior end down with a needle, 

 the head can be caught with the point of another needle and 

 pulled off. The glands, not being fastened posteriorly, will in 

 most cases draw cleanly out of the body. With larger larvae this is 

 not easy of accomplishment, and decapitation is the better method. 

 With the largest larvae, dissection from the dorsal side while im- 

 mersed in the fixative is best. Flemming's strong formula, 

 Tower's solution and 95 per cent, alcohol were most used, 

 as fixing agents. As described in previous papers, Vorhies ( 1 905 ), 

 Marshall and Vorhies (1906), Delafield's haematoxylin was most 

 satisfactory for whole mounts of the glands. The method of 

 splitting the glands previously described cannot, of course, be 

 used with the glands from larvae only 1.5 mm. to 2 mm. in length, 

 but the difficulties to be overcome by splitting in the larger glands 

 are in these not so great, therefore it does not matter. For sec- 

 tions, Flemming's triple stain, and iron haematoxylin were used 

 almost exclusively. Both sections and whole mounts were made 

 of the various stages, the whole mounts serving as a useful check 

 on the sections, and to show the changes in form of the nuclei. 



At the time of hatching the larvae of P. dcsignatus are about 



