THE SILKWORM ITS INTERNAL STRUCTURE. 35 



distinctly each by itself, if their form is to be properly seen and 

 their nature fully comprehended. It is this separation of the 

 different sets of organs from one another which is the object of 

 dissection. The process is a very simple one, and, with a little 

 care and delicacy of manipulation, is readily carried out. If 

 properly conducted, it is not, as some might suppose, in the least 

 degree a repulsive process, but. on the contrary, structures of 

 extraordinary delicacy and beauty are revealed, and a carefully 

 performed dissection will be found to possess considerable artistic 

 elegance. 



The study of the internal organization of the silkworm will 

 occupy us in the present chapter, but before we enter upon it. 

 it will be well to endeavour to form some idea as to what we may 

 expect to find in the interior of an animal standing, as our silk- 

 worm does, fairly high in the scale of organization. In order to 

 repair the waste that is ever going on in its body through the 

 performance of its vital functions, and to supply materials for its 

 destined increase in bulk, an animal needs to take in food, which 

 is the raw material out of which its frame is constructed. But the 

 food as taken in, though consisting chiefly of the right materials, 

 yet has them not in proper forms of combination, and its chemical 

 composition therefore needs to be altered ; the animal will con- 

 sequently require a set of apparatus, more or less complex, first 

 for the reception of the food, and secondly for its transformation 

 into a fluid of suitable chemical composition to enable it to act 

 as a body-forming and waste-repairing substance. This set of 

 apparatus is called the digestive system. But this fluid, thus 

 formed, will need distribution to the body at large, else it will 

 be of little use ; for waste and decay go on in all parts, and hence 

 repair must be equally widespread. The apparatus which provides 

 for the distribution of this formative fluid is called the circulatory 

 system. In its passage through the body, this fluid not only parts 

 with much of the nutriment it contains, but also receives into itself 

 certain waste products of a gaseous nature whereby it is rendered 

 unfit to perform its task ; these can be got rid of by simple 

 exposure to the air; there will be necessary, therefore, some 

 apparatus by which the fluids of the body can be brought into 

 contact with the atmospheric air, and this is called the respiratory 

 system. Certain other waste products are to be got rid of as 

 liquids, and for this purpose an excretory system is required. The 

 animal is, further, to be put into relation with the world around 

 it, by means of some apparatus through which it can receive 

 information from that world, and regulate its own actions accord 

 ingly. The set of organs designed for this use is called the 



