CIRCULATION OF THE BLOOD. 409 



adopt a motion of the juices in the germ en of the wings in the pupa of 

 some Lepidoptera, from the result of several of his experiments. 



241. 



After such facts, I consider the asserted circulation of the juices as 

 proved. Carus was formerly inclined * to limit the circulation to those 

 insects still in their stages of development, and therefore concluded that 

 it disappeared upon their transformation into the perfect state. This 

 opinion he subsequently gave upt, upon being convinced of the contrary 

 by his own experiments; and it also is positively contradictory to the 

 generally adopted physiological significance of the circulation, for what 

 in this respect is the case in young animals, must also be found in old 

 ones. Indeed it is true that in many insects an alteration takes place 

 in the reception of food, and its quantity becomes less, and that thence, 

 consequently, there must be found in them a slower digestion as well as 

 a smaller quantity of separated lymph, but it must not be forgotten, 

 that, precisely at this last period, the compass of the body is smaller, 

 whereas its internal organs are larger, and that these have already 

 attained their perfect development, and require but a small addition to 

 be retained in action ; and that, lastly, the whole internal cavity of the 

 body presents less free space in which the stream of blood can be 

 distributed. These various causes appear to me to explain the decrease 

 of the circulation ; and indeed in the higher animals the pulse is lower 

 in age than in youth ; wherefore, then, should not the same relations 

 be found in insects ? But that a circulation is found in these creatures 

 in their perfect state, is proved by direct observation ; must these, then, 

 be considered as exceptions to the rule, and that which is the rule in all 

 other animals, form the exception in insects ? I see no foundation for 

 such a conclusion. 



242. 



With respect to the physiological importance of the circulation in 

 insects, I conceive it consists especially in preserving a general motion 

 of the fluids, by means of which all the portions of it are subjected to 

 an equal deposition of oxygen. If the lymph passed through the 

 intestinal canal into the cavity of the abdomen, and remained there 

 stationary, those parts of it which encompassed the tracheae would 



* Entdeckung, &c., p. 21. f Nova Acta Phvs. Med. vol. xv. Pt. 2, }>. 14. 



