Respiration in Invertebrate Animals. 181 



vermiform in figure. A dorsal vessel carries the blood from the 

 tail to the head, a ventral in the reverse direction. The inter- 

 mediate currents invariably, in every species, bear from the latter 

 into the former vessel. This fact is perfectly patent to the eye 

 of every observer. The blood enters into the dorsal vessel from 

 the viscera, from the ventral trunk into the viscera. In sim- 

 plicity of mechanical principles nothing can exceed such an ar- 

 rangement. The annulose 'circulation^ observes two leading 

 directions, longitudinal and transverse. The dorsal trunk is 

 propulsive, the ventral distributive, the oesophageal ring con- 

 nective. Let the circulatory system of the articulated animal be 

 studied with reference to this comparative standard. 



Myriapodii, Insecta, Arachnida. 



These three classes are distinguished by one type of organi- 

 zation. The blood-system, the nervous, and the respiratory are 

 constructed upon one essential plan. A law, true of one, cannot 

 therefore suffer aberration in the other. The unity of nature's 

 constructive principles are observed with rigid in\iolability. The 

 lowest Myriapod is removed from the highest Annelid ouly by 

 a short distance : the former in the adult state has no chyl- 

 aqueous lluid, the latter no tracheal system. Is it mechanically 

 reasonable that the introduction of ' tracheae ' into the organism 

 should involve a radical change of plan in the orbital direction 

 of the blood-current ? It must be so, if Mr. Newport's expo- 

 sition of this subject be founded in truth. In the Annelid the 

 eye follows with clearness and certainty the currents in all the 

 lateral vessels attached to the dorsal trunk moving into or in the 

 direction of the latter. In what Mr. Newport has called the 

 systemic arteries in Myriapods and Arachnids, the blood moves 

 in a contraiy direction, from the dorsal vessel towards the viscera. 

 Those very vessels which in the Annelid can be proved indu- 

 bitably, by the eye, to be veins, are suddenly in the very next 

 class reversed into arteries ! Which is the more probable, — -that 

 her observers have perpetrated a paradox, or that nature has 

 reversed her course ? The subject deserves a more accurate 

 examination. 



All English and continental anatomists have implicitly followed 

 Mr. Newport ; where he is in error they are wrong, wliere he is 

 truthful tiiey are right. It is his exposition of this subject there- 

 fore that must be measured by the standard of actual nature. 

 Disciples will obey the master-teacher. 



Mr. Newport's rescurches on the " Circulation of the Blood" 

 in the Myriapods, Insects, and Arachnids, constituted a remark- 



