Respiration in Invertebrate Animals. 197 



be some stractural peculiarity which unfits them for tlie inter- 

 change of gases. There resides on the contrary in the walls of 

 the tracheae a marvellous endosmotic property, which enables 

 them to give passage in any direction to gaseous elements with 

 extraordinary facility. There occurs then in reality no example of 

 true branchial breathing in the larvae of Insects. It is only the 

 extracting of air from the water instead of directly from the 

 atmosphere*. The aquatic life of the Insect therefore is only ap- 

 parent, not real. The principle of the respiratory process is the 

 same whether in or out of the water, whether in the larva or 

 imago state, whether with internal trachese or external branchise. 

 There is no example of real aquatic breathing. 



A\Tiat light then do these anatomical minutiae reflect on the 

 question which involves the mechanism of nutrition and respira- 

 tion in the tracheary Articulata ? That is the question now to be 

 considered. It is surpassingly interesting. If the conclusions 

 which the author is about to present should prove to be exact, 

 the physiologist will have approached nearer to a solution of the 

 ultimate problem of respiration. He will see this function under 

 a new phase — under strikingly novel conditions. 



In all the transparent structures of Insects, such as the wings, 

 antennae, branchiae, &c., every observer may prove for himself 

 that the blood-currents travel in the same passages as the tracheae 

 (fig. 10, b, k, c). On closer scutiny it will be seen that a channel, 

 such as the nervure of the wings, bearing in its centre a large 

 tracheal tube (/c), exhibits on one side of this tube a current going 

 in one direction {b) ; on the other, another bearing in an opposite 

 course (c). These are afferent and efferent, arterial and venous 

 blood-streams. They are bounded by separate walls. The 

 afferent current is circumscribed by its own proper coats, the 

 efferent by its own ; and the trachea is placed intermediately, 

 having parietes quite distinct from, though contiguous to, those 

 of the blood-channels. This coincidence between the tracheae 

 and the blood-currents can be traced in the wings nowhere beyond 

 the Imiits of the nervures into the scaly spaces which they cir- 

 cumscribe. The returning of the corpuscles at a certain point 

 renders this fact quite unquestionable. Beyond this limit onlg 

 the fluid elements, not the corpuscles of the blood, extend. In 

 this extra- vascular region it is cgclosis, not circulation, which 



* M. Leon Dufoiir contends for the same principle : " Le dernier terme 

 de la composition organique serait done ici, comme dans les branchies des 

 Poissous, line trame vasculaire, en ne donnant a ce dernier mot que sa va- 

 leur rigourensement etymologiqne, c'est-u-dire anatomiqiie. Seulement 

 dans les Poissons c'est du sang, et dans les Insectes dc Vair, qui est renferme 

 dans les vaisseaux de cette trame." Ann. des Sc. Nat. 1852, torn. xvii. 



