36 SILKWORMS. 



nervous system. But this again necessitates another set of organs, 

 by means of which its movements may be effected in response 

 to the requirements indicated by the nervous system, and for this 

 purpose it must have a muscular system. Again, there are 

 sometimes certain special products which have to be separated 

 from the fluids of the body, not simply to be got rid of out of the 

 system, but for use in some way or other, either within the body 

 or outside, and the apparatus for this consists of secreting glands. 

 Lastly, provision must be made for the propagation of the race, 

 and therefore a set of reproductive organs is necessary. 



Bearing in mind these principles, let us take the full-grown 

 caterpillar as the most suitable subject for the investigation. 

 The first business is to kill it in such a manner as not to damage 

 it. This may be accomplished either by placing it under a glass 

 with a small piece of cotton wool on which a few drops of 

 chloroform have been dropped, or by immersing it in alcohol, 

 or spirits of wine, for a few moments. A little apparatus will 

 be required for the work of dissection ; but it is of such a simple 

 nature, that most of it can be easily prepared by the operator 

 himself. The dissection must be performed under water, as that 

 medium causes the various organs to float out from one another, 

 instead of lying in one undistinguishable heap, and enables them 

 to be more distinctly seen and more easily separated from one 

 another. A dish of some kind is therefore required. One of the 

 little oval white dishes which confectioners use for potted beef 

 (not the round ones) say about five or six inches long, or a small 

 rectangular tin box about four inches long, such as chemists sell 

 with glycerine jujubes will answer very well. This must be 

 supplied at the bottom with a layer of some substance, into which 

 pins may easily be stuck ; solid paraffin is about the best 

 material ; this may be obtained at the operative chemist's, or, 

 instead of this, an ordinary paraffin candle may be used. The 

 material is to be melted (say in an iron spoon over the gas) and 

 poured into the dish till a layer not less than a quarter of an inch 

 in thickness is produced, which will adhere to the bottom ; or the 

 solid substance may be laid in the dish in lumps, and then melted 

 by standing the dish in a pan of boiling water, when it will spread 

 itself out into a suitable layer and attach itself as before. It 

 adheres to the tin box much more readily than to the glazed 

 earthenware dish. It may then be stood aside till quite cold, 

 when it will be sufficiently hard to withstand pressure, but at the 

 same time soft enough to permit of pins being thrust into it. 



Cold water is then to be poured into the dish to the depth of 

 about an inch. Now it is ready to receive the body of the cater- 



