38 SILKWORMS. 



apparatus. They are useful for separating organs from one 

 another in places which the scissors and scalpel cannot reach. 



We will now suppose that we have all our apparatus in working 

 order ; in front of us, the dish with paraffin layer at bottom and 

 water above it, and the caterpillar firmly pinned down ; and at 

 our side, the forceps, scissors, scalpel, and needles, and a plentiful 

 supply of pins. A pocket-lens should also be kept near. If the 

 dissection has to be performed by artificial light, the rays from a 

 lamp should be directed upon the object by means of a bull's-eye, 

 otherwise it will be difficult to see the more delicate parts. 

 Suppose the caterpillar to be pinned out in the natural position 

 of crawling, back upwards. It will be a very good exercise to 

 make our first drawing of the creature as it is before dissection, 

 and to mark on the drawing the names of all the parts that are 

 visible outside. This done, we prepare for the actual dissection. 

 Holding the forceps in the left hand and the scissors in the right, 

 with the former we seize gently a tiny portion of the skin of the 

 back, and with the latter cut a slit in the skin from one end of the 

 body to the other. The slit must be cut in the skin only, and we 

 must be very careful not to injure the parts beneath, so that only 

 the extreme tips of the scissors must be used. Next a transverse 

 slit may be made at each end of this, on each side of it, and the 

 skin then gently separated on each side from the underlying 

 organs by means of the scalpel or needles, the skin itself being 

 still held by the forceps. When it is well separated on each side, 

 it may be pinned down to the paraffin along its edges, the pins 

 being inserted in a sloping manner, and in such a way that their 

 heads shall point away from the dissection, and thus not impede 

 the hands and tools of the operator. 



In this way, all the interior of the creature's body will be laid 

 open, but at first little can be made out of the organs it contains. 

 This arises from the fact that a good deal of the space just under- 

 neath the skin is occupied by a quantity of a whitish substance 

 arranged in the form of crinkled folds or frills, or something like 

 rather solid lace-work. This is called the "fat body," and 

 according to the degree of its development, it more or less 

 obscures the other parts. It constitutes a store of reserve material, 

 and is found only during the caterpillar stage. It is produced by 

 the extravagant eating of the larva, which takes in more food than 

 is requisite for present needs, and the superabundance goes 

 towards the formation of the " fat body," which will again be 

 utilised during the final transformations of the insect. 



In all probability, notwithstanding every precaution taken to 

 guard against cutting through more than the mere skin, the 



