340 LEWIS HENRY GOrGH. 



An Account of the Histology of Avitellixa centripuxc- 



TATA (RiVOLTA) . 



Avitellina ccntripuiictata (Rivolta) is on account of 

 the large size of its histological elements and the loosenesss 

 of their arrangement, exceptionally favourable for study. 



The best results Avere obtained from worms fixed with 

 Zenker's solution. 1 allow the solution to act for at least 

 six hours, then I transfer the specimens to running Avater for 

 twenty-four hours, after which they are carried through 

 alcohol 25 per cent, and 50 per cent., remaining in each for 

 at least three hours, being finally preserved in alcohol 

 75 per cent. 



In order to obtain the worms as expanded as possible, I 

 iisually hold them up with a pincette, allowing them to hang 

 free in the air; this almost instantly causes them to expand 

 on account of their own weight, when I suddenly plunge them 

 into the fluid, lifting them out at once ; after letting them 

 hang again for a few seconds I finally deposit them in the 

 reagent. The womns treated in this Avay fix in a fairly 

 expanded condition, and are not contorted or twisted. It is 

 of great importance, however, to obtain the specimens alive, 

 and they ought not to be washed previous to fixing. It is 

 not necessary to use iodine to remove the last traces of subli- 

 mate from material treated in the m.auuer described. 



I have used sublimate, formalin, and silver nitrate, as well 

 as Zenker, but no other reagent I know is to be compared 

 with Zenker's solution for fixing cestodes. It is specially 

 favourable for the study of the subcuticula and its connec- 

 tion with the muscles. 



Staining was performed with Ehrlich's hfematoxylin and 

 orange 6, which gives wonderfully clear pictures of the sub- 

 cuticula and muscles. For the study of the eggs, and the 

 changes taking place before maturation and fertilisation, I 

 recommend iron-haematoxylin and eosin. Tin's combination 

 also presents the best results for the flame-cells and the 

 nephridial cells surrounding the dorsal canal, and also shows 



