HABDWICKE'S SCIENCE-GOSSIP. 



[Aran, 1, 1367. 



divisible into three great but subordinate sciences — 

 morphology, physiology, and distribution, each of 

 which may, to a very great extent, be studied inde- 

 pendently of the other. 



Zoological morphology is the doctrine of animal 

 form or structure. Anatomy is one of its branches, 

 development is another ; while classification is the 

 expression of the relations which different animals 

 bear to one another, in respect of their anatomy and 

 their development. 



Zoological distribution is the study of animals in 

 relation to the terrestrial conditions which obtain 

 now, or have obtained at any previous epoch of the 

 earth's history. 



Zoological physiology, lastly, is the doctrine of 

 the functions or actions of animals. It regards 

 animal bodies as machines impelled by certain 

 forces, and performing an amount of work, which 

 can be expressed in terms of the ordinary forces of 

 nature. The final object of physiology is to deduce 

 the facts of morphology on the one hand, and those 

 of distribution on the other, from the laws of the 

 molecular forces of matter. 



Such is the scope of zoology. But if I were to 

 content myself with the enunciation of these dry 

 definitions, I should ill exemplify that method of 

 studying this branch of physical science, which it is 

 my chief business to recommend. Let us turn 

 away, then, from abstract definitions. Let us take 

 some concrete living thing, some animal (the 

 commoner the better), and let us see how the appli- 

 cation of common sense and common logic to the 

 obvious facts it presents inevitably leads us into all 

 these branches of zoological science. 



I will suppose that I have before me a lobster. 

 "When I examine it, what appears to be the most 

 striking character it presents? Why, I observe 

 that this part which we call the tail of the lobster 

 is made up of six distinct hard rings and a seventh 

 terminal piece. If I separate one of the middle 

 rings, say the third, I find it carries upon its under 

 surface a pair of limbs or appendages, each of 

 which consists of a stalk and two terminal pieces. 



If I now take the fourth ring I find it has the 

 same structure, and so have the fifth and the 

 second ; so that in each of these divisions of the 

 tail I find parts which correspond with one another, 

 a ring and two appendages ; and in each appendage 

 a stalk and two end pieces. These corresponding 

 parts arc called, in the technical language of 

 anatomy, " homologous parts." The ring of the 

 third division is the "homologue" of the ring of 

 the fifth ; the appendage of the former is the homo- 

 logue of the appendage of the latter. And as each 

 division exhibits corresponding parts in correspond- 

 ing places, we say that all the divisions are con- 

 structed upon the same plan. But now let us 

 consider the sixth division. It is similar to, and yet 

 different from, the others. The ring is essentially 



the same as in the other divisions ; but the appen- 

 dages look at first as if they were very different ; 

 and yet when we regard them closely, what do we 

 find ? A stalk and two terminal divisions exactly 

 as in the others, but the stalk is very short and 

 very thick, the terminal divisions are very broad 

 and flat, and one of them is divided into two 

 pieces. 



I may say, therefore, that the sixth segment is 

 like the others in plan, but that it is modified in its 

 details. 



The first segment is like the others, so far as its 

 ring is concerned ; and though its appendages differ 

 from any of those yet examined in the simplicity of 

 their structure, parts corresponding with the stem 

 and one of the divisions of the appendages of the 

 other segments can be readily discerned in them. 



Thus it appears that the lobster's tail is composed 

 of a series of segments which are fundamentally 

 similar, though each presents peculiar modifications 

 of the plan common to all. But when I turn to the 

 fore part of the body, I see at first nothing but a 

 great shield-like shell, called technically the " cara- 

 pace," ending in front in a sharp spine, on either 

 side of which are the curious compound eyes, set 

 upon the ends of stout moveable stalks. Behind 

 these, on the under side of the body, are two pairs 

 of long feelers or antennaj, followed by six pairs of 

 jaws, folded against one another over the mouth, 

 and five pairs of legs, the foremost of these being 

 the great pinchers or claws of the lobster. 



It looks at first a little hopeless to attempt to 

 find in this complex mass a series of rings, each 

 with its pair of appendages, such as I have shown 

 you in the abdomen, and yet it is not difficult to 

 demonstrate their existence. Strip off the legs, and 

 you will find that each pair is attached to a very 

 definite segment of the under wall of the body ; 

 but these segments, instead of being the lower 

 parts of free rings, as in the tail, are such parts of 

 rings which are all solidly united and bound to- 

 gether ; and the like is true of the jaws, the feelers, 

 and the eye-stalks, every pair of which is borne 

 upon its own special segment. Thus the conclusion 

 is gradually forced upon us that the body of the 

 lobster is composed of as many rings as there are 

 pairs of appendages, namely, twenty in all, but that 

 the six hindmost rings remain free and moveable, 

 while the fourteen front rings become firmly sol- 

 dered together, their backs forming one continuous 

 shield — the carapace. 



Unity of plan, diversity in execution, is the lesson 

 taught by the study of the rings of the body ; and 

 the same instruction is given still more emphatically 

 by the appendages. If I examine the outermost 

 jaw, I find it consists of three distinct portions— an 

 inner, a middle, and an outer, mounted upon a 

 common stem ; and if 1 compare tihs jaw with the 

 legs behind it or the jaws in front of it, I find it 



