MOEPIIOLOGT OF CYCLOPS. 3 



doublet of 3'" focus. The hard parts are best seen in water after treatment of the fresh 

 animal with ammonia. 



Eor preservation I follow Gieshrecht's method : kill with a few drops of osmic acid 

 (1 per cent.), decant the liquid Avhen tlie animals are dead and have sunk, wash in fresh 

 water and replace by alcohols successively of 30, 50, 70, 90 per cent., and absolute, at a])out 

 ten minutes' interval. The animals are now ready for staining, which may be done by 

 Mayer's saturated tincture of cochineal in 70 per cent. spirit(after a preliminary immersion 

 in spirit of that grade), or Kleinenberg's hiiematoxylin, of which I use an old dark sample 

 thinned with absolute alcohol and filtered*. After staining and removing to absolute 

 alcoliol tliey can be transferred for dissection to oil of cloves or glycerine by subsidence 

 (after Gieshrecht's method), or for imbedding to xylol, by adding first a few drops of 

 xylol, pouring off part of the liquid, and adding xylol and so on till they are in pure 

 xylol. By adding paraffin little by little to the xylol, keeping the solution just melted, 

 and replacing by fresh paraffin the imbedding is completed. For arrangement I pour 

 the paraffin and Cyclops on to a slide wet with glycerine, and then with a hot wire melt 

 the tiny slab upon the block of paraffin to fit the clamp of the microtome. For fixing 

 the sections, I have, unfortunately, not succeeded in making the shellac t or the india- 

 rubber process a certainty, and some of my slides only a few months old mounted with 

 india-rubber are already showing round pale .spots, a beautifully fenestrate structure in 

 the rubber film, which interferes with observation. One more word on staining : on the 

 whole, hasmatoxylin is the better ; but the cochineal runs it close, especially when the 

 osmic acid has distinctly browned the specimen, the resulting colours varying from 

 brick-red to chocolate-brown or violet, much like gold chloride. The darker ones are best 

 for the nervous system, but the nuclei of the other tissues show better in the redder ones : 

 in glycerine this colour washes out greatly, especially if the tinge be of the redder grade. 

 Gold chloride I have used with moderate success, owing to the tendency of the soft 

 structures to shrink from the cuticle, and have been hence unable to use picric acid or 

 borax-carmine ; but for the rapid staining, under the cover, of dissections of specimens 

 freshly killed with osmic acid, I have found diluted glycerine and picrocarmiuc a 

 useful medium. 



Genus CYCLOPS, O. F. Miiller. 

 Inner maxillipeds not markedly subchelate (fresh water). 



Species Cyclops brevicornis, Glaus. 



Antennulcs of female l7-jointed, comparatively short and blunt, not extending beyond 

 its free thoracic segment; 5th thoracic foot 2-joiuted, bearing 2 plumes and a short tooth ; 

 size 2'5-55 millim. 



Claus gives the size of Cyclops bi-evicornis as 3-5 millim., of C. (jUjas 5-5 ; Brady gives 

 C. gigas as 2'7 millim. I have found it vary from 2-5 to 3'S millim. 



* In all work with alcoholic stains I make a point of immersing tho specimen in alcohol of the same grade as 

 the solvent, both before and after staining, to avoid all chance of precipitation. 



t At least half my attempts with shellac have resulted in tho scattering of the sections, or else in a spottiness of 

 the shellac. [I have since devised a successful improvement on the sheUac method. — June 1887.] 



1* 



