ON THE ANATOMY OF HISTKIOBDELLA HOMAKI. 28^ 



to be added to the water from time to time. Witli good air- 

 circulation and a little attentioii, a medium-sized lobster can 

 be kept alive for several weeks in a tank of four or five litres 

 capacity without change of water. 



At the end of the second day the blue will have collected 

 in dark granules on the walls of the iiephridial canalsj so as 

 to outline these clearly. By this time it has been discharged 

 from the nervous system and the sensory cells of the 

 epidermis. About the bases of the legs of the head it shows 

 a tendency to remain some time after it has disappeared from 

 the brain. It is retained alone by the nephridia on the third 

 day. Here it collects in dense masses on the courses and 

 openings of the canals. 



In the study of these methyl-blue preparations I have 

 made use of long, thin cover-slips, such as are used in pre- 

 paring large serial sections instead of ordinary slides, on 

 which to mount my preparations. The use of a thin cover- j 

 slip used as a slide allows of the propai-ation being examined 

 from each surface, as desired, under an oil-immersion lens. 

 It is thus possible to trace a nephridium first on one side of 

 the preparation, and then turn the slide over and trace it 

 further on the other surface. 



Histriobdella is a somewhat difficult animal to fix. The 

 only reagent that has given uniform results is a saturated 

 sublimate solution, with 5 per cent, acetic, used boiling hot. 

 Hermann's solution and Flemming and the osmic acid 

 mixtures give very irregular results, and are not to be 

 depended on for their action. One lot of material will be 

 excellent, while the next, fixed with the same solutions and 

 under the same conditions, are useless. Picro-acetic and 

 Bouin's solutions, used hot, give good results, but not as good 

 as material fixed with sublimate-acetic. Picro-sulphuric was 

 used for preparations to be studied whole, on account of the 

 excellent preservation it gives of the external form. As 

 stains, the following have given satisfaction : Heemacalcium 

 and Benda's iron-htematoxylin, paracarmine, lithium-carmine 

 followed by Lyon's blue for eggs. 



