84 PROCEEDINGS OF THE ACADEMY OF [Feb., 



{lifferentiation of the nerve fibres became evident. Tlie latter did not 

 absorb the chromatin stain (iron-hsematoxylin), but on the contrary 

 remained clear and of a light straw yellow color, or, in sections where 

 eosin was used as a contrast stain, were pale orange. In either case 

 the nerve fibres are easily distinguished from the surrounding tissues. 

 What happy accident caused this differentiation, which occurs in all 

 the series made from the second lot of individuals, I have not been able 

 to determine. It has, however, been of the highest value to me, since 

 without its assistance it would have been an extremely difficult matter 

 to trace out the various parts of the nervous system. That it is but 

 an accident I feel sure, since a number of individuals of another lot, 

 fixed and stained by the same method, showed the nerve fibres stained 

 dark gray, as is the case where other fixatives were used. 



(3) Flemming's fluid, from one-half to twenty-four hours. This 

 method gave very irregular results, yielding some of the finest prepara- 

 tions, as well as some of the poorest. Different individuals, even of 

 the same lot, vary much in the quality of the fixation. The best 

 results were obtained with a fixation of half an hour, although the 

 period of fixation seems to be of minor consequence, since good results 

 were also obtained with a fixation period as long as twenty-four hours. 



The stains employed were: the picro-hcematoxylin of Conklin (1902) 

 for the objects mounted entire, and Haidenhein's iron-hsematoxylin 

 for sections. A contrast stain was used in some cases, a saturated 

 aqueous solution of eosin being employed for this purpose. Experi- 

 ■ence, however, has shown that the use of a plasma stain wdth the iron- 

 lia^matoxylin is, in this form at least, unnecessary, if not actually 

 undesirable. For the purpose of determining the presence of mucin 

 in the hypodermis, Mayer's mucicarmine was employed. The formula 

 is that given by Lee in the fifth edition of The Microtomisf s Vade- 

 Mecum, the material being stained from five to fifteen minutes in a 10 

 per cent, solution. 



The sections were for the most part cut five fi in thickness, this 

 being found to be the minimum compatible with perfect series. Many 

 of the DinopJtilus were embedded and oriented separately, but the 

 best horizontal and sagittal series were obtained by embedding a large 

 number in a Lefevre watch glass, and sectioning the mass entire. 



The living animals were also studied, but, on account of the refrac- 

 tive nature of the protoplasm, proved very imfavorable objects, as far 

 as the internal structure was concerned. Narcotization was success- 

 fully accomplished b}^ the use of chlorotone, the animals soon becoming 

 quiescent, in a relaxed condition, tying on one side, with a shght 

 ventral flexure. 



