APPENDIX. 471 



mouth is wide open looks not unlike a wheel, the tentacles 

 being the spokes ; but if, as is often the case, the 

 sphincter contracted at death, it will lie on its side, 

 appearing as a cone with the tentacles at the apex. In 

 removing the dorsal portions of the myotomes, the yellow 

 notochord will bo exposed. Dorsal to this lies the spinal 

 cord, which needs some scraping to be fully exposed : it 

 shows as a very thin white line ; with a lens the row of 

 pigment-spots is plainly seen. The dorsal fin-rays are 

 also very noticeable. The dissection of the spinal cord 

 may be made much easier if the whole animal is soaked 

 for a day or two in 20 per cent, nitric acid and washed. It 

 is possible then to completely isolate the spinal cord 

 and mount it the dorsal and ventral nerves and pigment- 

 spots are well shown. To see the skeleton of the 

 pharynx a piece should be cut out, laid open on a glass 

 slide and mounted in caustic potash solution, with a 

 cover-glass. 



Young specimens of Amphioxus can be had mounted 

 whole for microscopic examination. These differ from the 

 adults in that the gill-slits are few and simple, and the 

 gonads undeveloped. 



In the earthworm the finding of the ovary gives much 

 trouble to beginners. The following method is recom- 

 mended. Cut across the beginning of the intestine ; grip 

 the gizzard with forceps (it is the only part of the alimen- 

 tary canal that will stand handling), lift it up and cut the 

 septa beneath it. Work forwards in this way, carefully 

 cutting each septum in turn with a sharp scalpel on both 

 sides of the middle line. Gut them also between the 

 oesophagus and the seminal vesicles, or you are likely to 

 tear away the latter. In this way you can remove a con- 

 siderable part of the alimentary canal. It is also well to 

 pin out the posterior pair of seminal vesicles, or they may 

 lap back and hide the ovaries. The ovaries should now 

 be visible to the naked eye in Segment 13, a little on 

 either side of the nerve-cord. 



For the remaining types, we do not think any special advice is 

 needed. We may, however, mention some of the most conspicuous 

 and common internal parasites, which are likely to puzzle the 

 solitary worker. The rabhit frequently has clear spherical bodies. 



