300 SUMMARY OF CURRENT RESEARCHES RELATING TO 



insure rapidity of hardening it is well to remove a part of the chitinous^ 

 membrane, after the animal has been for a few minutes in the fluid. 

 Sublimate and alcohol with a drop of nitric acid were used for hardening 

 the free enteric canal ; for the examination of the eyes use was made of 

 Grenacher's depigmenting mixtures. The staining of sections, which 

 were fixed to the slides by Meijer's albumen, gave better results than 

 staining the whole animal or parts thereof; Weigert's picrocarmine, alum- 

 carmine, and others were used, but hsematoxylin gave the best results. 



Method of investigating Cyclops.* — In his researches into the 

 morphology of Cyclops Prof. M. M. Hartog sometimes found it necessary 

 to examine living specimens ; undue pressure was avoided by putting 

 under the cover a frond or two of Lemna ; this arrangement has the 

 advantage that by a push at the edge of the cover the Cyclops can be 

 rolled over. The Abbe condenser was found invaluable. For dissec- 

 tion, French spear-head needles were used ; the hard parts are best seen 

 in water after treatment of the fresh animal with ammonia. For pre- 

 servation Giesbrecht's method was used ; staining was effected with 

 Mayer's saturated tincture of cochineal in 70 per cent, spirit, or Klein- 

 enberg's hfematoxylin. For imbedding xylol was used, and paraffin 

 little by little added. Hsematoxylin is to be preferred for staining, but 

 cochineal runs it close, especially when osmic acid has distinctly 

 browned the specimen, the resulting colours varying from brick-red to 

 chocolate-brown or violet, much like gold chloride. The last-named 

 reagent was not very successful, ovs^ing to the tendency of the soft struc- 

 tures to shrink from the cuticle ; for rapid staining diluted glycerin and 

 picrocarmine is a useful medium. 



Examination of Nematodes-j — Herr N. A. Cobb states that he 

 obtained the most instructive results by dissecting Nematodes under the 

 dissecting Microscope with a needle and a small knife about 1 mm. 

 broad. It is best to cut along the lateral areas. For the examination 

 of the central nervous system of the larger species he took about half a 

 centimetre of the front end of the body and divided it by a longitudinal 

 section in such a way as to get two lateral or, in other cases, dorsal and 

 ventral halves. After removing the oesophagus the pieces were stained 

 and imbedded in Canada balsam. In the case of the smaller free-living 

 species, which it was impossible to dissect, they were either examined 

 alive or after treatment with 1 per cent, osmic acid ; the nervous system 

 was most distinct after two or three hours' treatment. A compressorium 

 was sometimes necessary ; in its place the use of the following process 

 was often found to be attended with good results. The worm was 

 placed in a drop on a slide ; two fine hairs were laid on either side of 

 the drop, and over it a large cover-glass. If the drop of water was not 

 sufficient to fi.ll the space between the slide and the glass the animal 

 could be squeezed between the slide and the cover-glass, and its position 

 altered as might be required by moving the latter. 



The preparation of good sections of large Nematodes is not easy, as, 

 after imbedding in paraffin, the object becomes very hard, and sections 

 difficult to cut ; in fact, it became evident that good sections could not 

 be obtained in the ordinary way. At last Herr Cobb set his razor per- 

 pendicularly to the path of the microtome and cut as quickly as possible ; 



* Trans. Linn. Soc. Lond.— Zool,, v. (1888) pp. 2-3. 



t Jenaisch. Zeitschr. f. Naturwiss., xxiii. (1888) pp. 42-3. 



