THE OSTRA( ODA Ro^ 



finest needle is scarcely efficient as a dissecting instrument. T - 

 of the above two mounting media bring out to view even the ..... l 

 hairs or ciliated structures. Alcohol or water are not advisable as 

 dissecting media and should be risked with few specimens. Fur- 

 thermore, Farrant's medium makes a very good permanent mount, 

 providing there is not too much on the slide. Kither medium 

 should be added to the slide in small drops, then spread out in a 

 thin layer before attempting to dissect therein. It is commonly 

 best to make a preliminary examination of the di«»scclion with a 

 f-inch objective, to see that the mount has been well prci)arcd 

 and arranged. If so, add a small additional amount of the me- 

 dium, cover with cover glass, and the mount is permanent, pro- 

 vided the work is neatly done, too much medium is not added, and 

 the mounts are kept stored in a horizontal position when not in use. 



The valves should be preserved entire, if possible, and removed 

 to one side of the slide for further study. It is often (le^iral)le that 

 they be removed to a separate slide and mounted in b.d-.un, es- 

 pecially if the slides are to be permanent and subject to muth 

 handling. 



Drawings as well as study of a side view should always Ik- made 

 from one of the valves, rather than from the entire sixi'imcn. as 

 otherwise a distorted view is likely to result. 



The dorsal view is more difficult to get - indeed, it is often 

 advisable not to attempt it. Unless this view is obtained directly 

 above the specimen, it is worthless. Sometimes one valve alone 

 may be used by fastening it to a needle or similar object, and 

 then studying while covered with glycerin, or. it the valve> arc 

 dissimilar the entire animal may thus be mounted so that an 

 exact profile may possibly be obtained. It is indeed often i^^- 

 sible to get very good dorsal profdes from many six-cimens while 

 they are in alcohol and glycerin in a s>Tacusc watch ghuv«i. 



The following characters have been retained as of most value 

 in the following key: presence and length of natatory sc-tae of 

 the second antennae, segmentation of the second antennae, form 

 and number of spines of the first n.axillary i>rocess. armature ol 

 the second leg, arrangement of the spennatic gland, and armature 

 and shape of the furca. 



