APPENDIX 555 



upon the coverslip the dimness will be affected by moving the 

 slide ; if it be upon the ocular, by turning the latter ; if neither 

 of these be in fault the objective is dirty. In a wet prepara- 

 tion a dirty coverslip must be replaced ; a dry one may be 

 cleaned in the same way as the objective. 



5. If the tube will not slide freely, it or the inside of the collar 



tube which holds it is dirty. They may be cleaned by careful 

 but vigorous rubbing with a dry duster. 



6. Keep both eyes open in looking through the microscope. 



The following is an outline of the procedure which should be followed 

 in the practical examination of an animal : — 

 How to Examine I. Examine alive, as recommended above. 

 an Animal. 2. Make a drawing of the external features. These 



are generally best shown in a side view. 



3. Make separate drawings of parts, such as limbs, the mouth, etc., 



which are not fully shown in your first drawing. In the case 

 of the crayfish and cockroach this will involve several drawings 

 of appendages. 



4. If the animal have a perivisceral cavity in which the organs lie 



free, open this cavity and make a drawing of the organs in situ 

 without disarrangement. Vertebrates should be opened on 

 the ventral side, invertebrates on the dorsal. If the body- wall 

 be hard, as in the crayfish and cockroach, it may be removed 

 as a single piece after two lateral incisions ; if it be soft, a 

 median incision should be made, and the body-wall turned 

 back or reflected to each side and pinned out. In a verte- 

 brate the skin and the muscular body-wall must generally be 

 turned over separately. The thorax of a mammal should not 

 be opened till a later stage, and the relation of the organs and 

 cavities should be observed carefully during the process. 



5. Remove the alimentary canal by cutting through its ends, and 



the mesentery if there be one. Draw (a) the removed canal, 

 (i) the body cavity with the organs left behind. In the cray- 

 fish, the endophragmal skeleton must be cut away in order to 

 show the nerve cord. 



6. In a vertebrate, make a special dissection of the heart, the great 



vessels entering and leaving it, and the respiratory organs. 

 Make a drawing. 



7. In a vertebrate, make a dissection of the organs of the neck and 



throat from the ventral side. Draw. 



8. Expose the brain or cerebral ganglia, and examine it in situ with 



its nerves. Draw. Remove, and draw dorsal and ventral 

 views. Ninety per cent, alcohol is useful in whitening and 

 hardening the nervous system. 



9. In a vertebrate, make a series of drawings of the parts of the 



skeleton. Skeletons may be prepared by removing most of 

 the flesh and boiling or macerating (i.e. placing in water and 

 allowing the flesh to rot). They should then be washed 

 thoroughly and bleached in sunlight. Cartilaginous skeletons, 

 however, should not be rotted or allowed to dry, but dipped 

 into hot water for a few minutes and cleaned with a brush. 



