CONSTITUTION OF THE ANIMAL AND PLANT KINGDOMS. 41 



plan. So that, although the amalgamated joints of the animal's head 

 and chest (Fig. 2, ca) are seemingly different from those of its tail 

 (Fig. 2, 1-6), the zoologist could readily show the uniformity of the 

 series by a comparatively simple disse'ction, 

 wherein, aided by the knowledge of the 

 animal's development, legs, "nippers," jaws, 

 feelers, and even eye-stalks would be referred 

 to modifications of one and the same type. 

 Furthermore, our dissection of the lobster 

 would show that, whilst its heart (Fig, 3, n) 

 lies on its back, its digestive system (sf) runs 

 through the middle line of its frame ; and its 

 nervous system (e, g), in the characteristic 

 form of an essentially double chain of nerve- 

 knots, lies on the floor of its body. So that 

 we might diagrammatise with strict accuracy 

 the essential build of a lobster's body by con- 

 structing a jointed figure (Fig. 4), wherein the 

 heart (a) lay highest, the nervous system (c) 

 lowest, and the digestive system (b) between 

 the two. 



Now this figure, it may be remarked, would 

 accurately represent every known lobster. It 

 would also stand for the essential structure of 

 every crab which is merely a tailless lobster 

 and of every shrimp, barnacle, water-flea, 

 slater, and a host of allied animals as well. 



Turning now to the butterfly, we should dis- FIG. 2. JOINTS OF LOBSTER'S 

 cover from even a rough examination of the 



insect's frame that it possesses an essentially similar disposition of 

 parts to those of the lobster. The butterfly's heart lies on its back, 

 its digestive system occupies the middle position, and its nervous 

 system lies on the floor 

 of the body, and more- 

 over consists of the same 

 knotted and double chain 

 we see in the lobster. 

 Again, the appendages of 

 the butterfly-body are in 

 pairs, and resemble those 

 of the lobster in all essen- 

 tial particulars, although 

 they are less numerous, 

 in the adult state at least. 



FIG. 3. DIAGRAM OF LOBSTER'S STRUCTURE. 



So that, beyond and beneath all differences 



in appearance, form, and habits material as these differences appear 



