Journal of Applied Microscopy. 295 



sections of teeth three inches in length and less than jTrVo ^^^^^ thick by this 

 method. The same method can be used for any ground sections, applying of 

 course suitable modifications, e. g., spines of Echinie, soft and hard tissues 

 imbedded according to Von Koch or Weil, minerals, etc. 



S. P. COWARDIN. 

 March ist, 1899. 



Methods of Making Microscopic Preparations of Copepoda. 



Although the copepods are present everywhere and are very easily collected, 

 few books, so far as I know, give directions for preparing and mounting them 

 for the microscope. It is true that the dissection of these minute animals 

 requires much patience and some skill, but many more difficult operations are 

 undertaken even by amateurs. It seems a little strange, therefore, that there 

 are so few students who have even an elementary knowledge of them. 



Copepoda and entomostraca in general are most easily collected by means of 

 the dredge devised by Professor Birge, the essential part of which is the mouth 

 covered with a cone of coarse wire gauze. This gauze-covered mouth keeps out 

 the sticks, weeds, etc., which otherwise would immediately fill the net, so that 

 the net can be repeatedly drawn through a weedy pond, and a large collection 

 can be made which is comparatively free from de'bris. 



If the copepods are to be used for histological purposes, they should be 

 killed by some one of the osmic acid preparations. If, however, they are to be 

 used for systematic purposes, or for the study of the muscles, I have found no 

 killing and preserving agent so good as alcohol. Formalin leaves the material 

 brittle and unfitted for dissection, and is, besides, excessively disagreeable to the 

 one who has to work over it. The collection can be placed immediately in 

 alcohol, the water which will go with it diluting it sufficiently, and nothing 

 further need be done with it until one is ready to study the material. 



In order to stain the material, most of the alcohol should be withdrawn by 

 means of a pipette, and a little picro-carmine put into the bottle. The best 

 results are obtained by a somewhat prolonged exposure to a dilute stain — from 

 one to three days. Anilin stains may be used, but picro-carmine is more 

 satisfactory. For a systematic study of the copepoda, it is necessary to dissect 

 off the various appendages and mount them in order. This requires a great 

 deal of patience and a steady hand. I suppose that it is this work which deters 

 so many from attempting to do anything with these animals. The dissection 

 must be done on the slide, and, inasmuch as alcohol evaporates very rapidly, it 

 is best to replace the alcohol with glycerine. This change from alcohol to 

 glycerine must be made very gradually, or the specimen will be distorted and 

 perhaps ruined. The finest needles must be used for the dissection, and better 

 work can be done if the needles are carefully ground down on two sides so as 

 to make minute scalpels. 



The work of dissection on the larger forms can be readily carried on under 

 an ordinary dissecting lens, but for the smaller forms it is almost necessarj' to 



