Respiration in Invertebrate Animals. 199 



element travels forwards to operate immediately, in its wnexhausted 

 form, on the final elements which conspire to maintain the nu- 

 trition of the living body. 



The intense electrical and chemical effects developed by the 

 immediate presence of oxygen, in the gaseous form, at the actual 

 scene of all the nutritive operations of the body, fluid and solid, 

 give to the insect its vivid and brilliant life, its matchless nervous 

 activity, its extreme muscularity, its voluntary power to augment 

 the animal heat ; such contrivance, subtle and unexampled, re- 

 conciles the paradox of a being microscopic in corporeal dimen- 

 sions and remarkable for the relative minuteness of the bulk 

 of its blood, sustaining a frame graceful in its littleness, yet 

 capable of prodigious mechanical results. 



EXPLANATION OF PLATES IX. and X. 

 Plate IX. 



Fig. 1 . Plan of the central parts of the circulatory system of the Myriapod, 

 constructed in part from Mr. New|)ort's figures and in part from 

 the author's dissections : a, d, the dorsal vessel ; the arrows mark 

 the direction of the blood ; b, the oesophageal collar ; cSf e, supra- 

 spinal artery ; /, the systemic arteries (sic) of Mr. Newport. 



Fig. 2. Plan of the central parts of the circulatory system of the Insect : 



a, dorsal vessel. The anterior or thoracic half is a smooth tube, 

 the abdominal chambered by valves ; b. the supraspinal ai-tery, 

 having on either side venous currents (c), as shown by the arrows ; 



d, branches, distributive, from the supraspinal artery ; e, large, 

 loose-walled venous channels entering the capacious abdominal 

 sinuses g, g ; f, the membranous channels which pour their blood 

 into the dorsal vessel at the auricular orifices. The blood in the 

 dorsal vessel moves forwards, that in the supraspinal artery moves 

 backwards. 



Fig. 3. a, p. Dorsal artery ; p, its caudal continuation ; d, its cephalic ; 



b, visceral arterj', sending distributive branches (i) into the viscera, 

 the blood of which is returned into the dorsal artery by n, n, the 

 systemic arteries of Mr. Newport; c, the supraspinal artery, 

 convej-ing blood to the nervous and integumentarj' structures ; 



e, subspinal vein ; /, branches going to the pneumo-branchiae {g) ; 

 h, origin of the pneumo-cardiac channels {k, k, k) ; I, continuation 

 of the subspinal vein into the tail ; m, branches commimicating 

 with the dorsal arterj- (p). 



Fig. 4. Glassy, jelly-hke aquatic larva of an Insect, common in the pools 

 about Swansea ; a (e), kidney-shaped tracheal vesicles, without 

 any ramifying tubes ; b, dorsal vessel ; d, arrows denoting the re- 

 turning into the dorsal vessel at the posterior auricles {b). 



Fig. 5. Aquatic larva of Sialis Lutarius : a, branchial appendages; B, one 

 of the branch ia; enlarged ; 6, trachea; ; c, cell-tissue. 



Fig. G. Aquatic larva of one of the LibelluUdte : a, branchial appendages ; 

 B, the same further enlarged ; b, trachea ; c, secondary arbo- 

 rescent branches ; C, extreme end of one of the tracheal bi*anclies 

 traced under a high power to its membranous capillary- termina- 

 tion/, (7. 



