350 On the Uses of the Dorsal P'essel [Nov. 



at least examined ourselves all the details of organization which we 

 have made known in our memoir. In this point of view it will 

 always have a real value. We must acknowledge that in the 

 anatomy of animals so small, and so difficult to dissect, it is almost 

 impossible to avoid falling into some errors. We ought to consider 

 it as fortunate when these are confined to details which have not a 

 great influence on the organization. It is in this point of view that 

 it is of importance to science that different observers study the same 

 subject. It is only in that way that we can be sure of having made 

 good observations. We cannot terminate what we have to say 

 respecting our researches without informing those who may be de- 

 voted to the same kind of labour that the best means of avoiding 

 errors is to dissect in water, as Cuvier has advised. It is proper 

 likewise to employ wires of copper and zinc to discover the nerves, 

 according to the method recommended by Humboldt. 



Insects have a longitudinal vessel along the back, which extends 

 from the upper part of their body to the other extremity, and to 

 which almost all anatomists have given the name of heart, in con- 

 sequence of the regular contractions and dilatations which it 

 exhibits. Lyonnet and Cuvier alone have started doubts respecting 

 the reality of the functions ascribed to this organ. The illustrious 

 author of the Comparative Anatomy is likewise the first who endea- 

 voured to prove that this heart has no sort of ramification. Lyonnet 

 had already remarked that no smaller vessel issues from the dorsal 

 vessel. But as he observed this fact only in the caterpillar of the 

 willow he did not venture to draw a general conclusion from an 

 observation which might be only particular. Yet, notwithstanding 

 the numerous proofs of all kinds accumulated by M. Cuvier in his 

 fine memoir on the nourishment of insects * against the existence 

 of a true heart in this order of animals, doubts still continue re- 

 specting this delicate question among a considerable number of 

 anatomists. To endeavour to destroy these we have entered into 

 some researches respecting this interesting point. 



We have turned our chief attention to the following questions : — 



1. It appeared to us essential to study the dorsal vessel in the 

 different orders of insects, in order to know whether it ever presented 

 ramifications, which might be expected in it, because Swammerdam 

 and Comparetti distinctly say that they observed them. Comparetti 

 has even described them somewhat in detail. 



2. If this first means proved insufficient, it was necessary to 

 ascertain whether they might not become visible by injections either 

 of mercury or coloured liquids, or astringent liquors, or such as by 

 their chemical properties are capable of acting upon the humor 

 contained in the dorsal vessel. Thus tannin, by coagulating that 

 humor, appeared capable of throwing some light on the uses of this 

 vessel, and of showing its ramifications, if any such existed. 



» Memoire sur la Maniere dont se fait la Nutrition dans les Tnsectcs, inserted in 

 the Memoirs of the Natural History Society of Paris, t. i. p. 34. 



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