MOEPHOLOGT OF CYCLOPS. 3 



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

 animal with ammonia. 



For preservation I follow Giesbrecht's method : kill with a few drops of osmic acid 

 (1 per cent.), decant the liquid when the 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 about 

 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 hematoxylin, of which I use an old dark sample 

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

 alcohol they can be transferred for dissection to oil of cloves or glycerine by subsidence 

 (after Giesbrecht'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, hematoxylin 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 citticle, 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 picrocarmine a 

 useful medium. 



Genus CYCLOPS, O. F. Miiller. 

 Inner maxillipeds not markedly subchelate (fresh water). 



Species Cyclops brevicornis, Claus. 

 Antennules of female 17-jointed, comparatively short and blunt, not extending beyond 

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

 size 2"5-5'5 rnillim. 



Claus gives the size of Cyclops brevicornis as 3-5 rnillim., of C. gigas 5-5 ; Brady gives 

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



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

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



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

 the shellac. [1 have since devised a successful improvement on the shellac method.— June 1SS7.] 



1* 



