68 



PROF. AGASSIZ S 



swellings; next, a great spacewithout lateral nerves; 

 and then, a space with swellings at equal distances, 

 corresponding to the abdomen. Remember now 

 the arrangement of rings and legs in the Caterpil- 

 lar and in the Grasshopper, [Plate XV], You will 

 see that the arrangement of the external parts 

 agrees with that of the nervous system. The 

 head consists of one undivided mass [Plate XV. 

 fig. A ] There are three pairs of horny claws in the 

 Caterpillars (Plates IX, X, and XI,) and three rings 

 to the chest in the Insects proper, (Plate XV, figs. 

 B, C, D) receiving nerves from the concentrated 

 swellings of the anterior part of the body. Then, 

 there is a region from which no nerves are deriv- 

 ed ; and a region from which four pair of sucker- 

 like legs are produced, answering to the region in 

 which these four swellings remain equally distant; 

 and then another region, of two rings without; and 

 another, last, with suctorial legs, which corres- 

 ponds to the large terminal nervous swelling. 



It is a question which it is not possible to solve 

 now, and which it will be very difficult to solve, if 

 it can be solved at all, whether the larger terminal 

 swelling of nervous matter consisted originally of 

 one nervous mass; and whether the anterior ce- 

 phalic ganglion consisted also, primitively, of one 

 nervous mass. That it consists of two now, is 

 shown here, [Plate XI. fig. A] by the entire disap- 

 pearance of the first small ganglion. But there 

 may be other changes in the structure of the ner- 

 vous system, taking place previous to the full 

 growth of the Caterpillar. And this remains for 

 the present undecided. But, so much is shown as 

 to prove that the nervous system is equally dis- 

 tributed in the solid rings, and they will gradually 

 combine in such a manner as to present arrange- 

 ments answering to the changes which take place 

 in the external form. There is one mass more, 

 properly belonging to the head, another mass more 

 concentrated, belonging to the chest, and another 

 mass remaining stationary and belonging to the 

 abdomen. 



We now can, with these facts, arrive at another 

 general conclusion, viz. : that wherever among ar- 

 ticulated animals, among Insects, we find the ner- 

 vous system constituted of equally distributed ner- 

 vous swellings, such animals are lower than those 

 in which several swellings unite together to form 

 few masses. Now, in this respect, what do we ob- 

 serve in the different classes compared together ? 

 I now no longer compare the same animal in 

 its different stages of growth, but different classes 

 of Articulata with each other. What do we observe 

 in comparing Insects with Worms,and Worms with 

 Crustacea 1 All worms have equal rings and very 

 numerous joints ; and joints which are never com- 

 bined so as to form regions distinct from each 

 other. There is never a distinct thorax or abdo- 

 men in any Worm. So that, from what we have 

 learned, we know that the lower position assigned, 

 for many and all sorts of good reasons, to worms, 

 is the - -T position which they must preserve ; 



and where a nervous system has been observed 

 among them, it agrees with the condition of that 

 system in Caterpillars, rather than with that of the 

 later metamorphoses. The question remains be- 

 tween Crustacea and Insects. What is the condi- 

 tion of the nervous system in Crustacea 1 ? The 

 nervous system occurs in various conditions there. 

 In the lower Crustacea,the swellings being scatter- 

 ed all along the body, one to each ring a condi- 

 tion which we observe in the earlier stages of 

 growth in the Caterpillar. Next, we have other 

 Crustacea in which the nervous swellings contract 

 and combine together, nearer and nearer. But in 

 them, strange to say, there is only one point of 

 concentration. And then there are Crustacea, as 

 the Crabs, in which the nervous system is con- 

 tracted into one single, central mass. And the 

 question is, what shall we consider superior? an 

 arrangement which gives rise to several distinct 

 centres, and corresponds to distinct regions of the 

 body, (as in Insects, Plate XII., fig. F. and Plate 

 XIV, fig. A) a head,with a central nervous swelling 

 of a peculiar kind ; a chest, with a nervous mass of 

 a peculiar kind, sending its thread to the legs of 

 that region ; and another posterior combination of 

 nervous swellings, corresponding to the other re- 

 gion, called abdomen, and sending nerves to its 

 part? 



It seems to me that we cannot remain doubtful. 

 We cannot fully derive this conclusion from direct 

 investigations, as we have not, in any instance, a 

 case to settle it by direct comparison ; but we may 

 say,that in Crustacea we have concentrated unifor- 

 mity; while in Insects in their perfect condition, 

 we have concentrated diversity. And, if we are al- 

 lowed to compare the one with the other, I would 

 incline to the opinion that concentrated diversity, 

 with prevailing influences over peculiar functions 

 of the life of the different centres, is a condition of 

 structure which stands higher than concentrated 

 uniformity ,in which we have only one centre. We 

 have all the primitive diversity reduced to one 

 centre, which does not acquire any distinct influ- 

 ence upon different parts. 



The alimentary canal undergoes corresponding 

 metamorphoses. Here is the straight tube (Plate 

 XIII, fig. A) of the digestive canal of a Caterpillar. 

 It is very wide in comparison to its length, and ca- 

 pable of digesting an immense mass of food, com- 

 paratively to the size of the animal. In its earlier 

 condition, it is provided with an apparatus which 

 disappears afterward. There are considerable sali- 

 vary glands in the anterior portion of the alimen- 

 tary canal, which disappear in the pupa state and 

 do not exist in the perfect insect. These figures 

 (Plate XIII) must impress you as very singular. 

 No animal has more curious organs than this In- 

 sect. The liver, or hepatic glands, and the salivary 

 glands are massive organs in other animals. Here, 

 they are slender tubes, and form little winding 

 branches on the sides of the alimentary tube. In- 

 eed, all glandular organs in Insects have such a 



