1891.] -1 new Mode of Respiration in the Myriapoda. 201 



branous towards the end, affording a good opportunity for inter- 

 change of gases. 



3. The tube ends project into the pericardium, so that they are 

 bathed with the blood. 



4. The tubes are filled with air. 



5. The organ is so placed as to aerate the blood just before it 

 returns to the heart. 



6. In Scutigera the dorsal scales do not agree in number with the 

 legs. The organs are arranged on the dorsal scales ; that is they are 

 not arranged in correspondence with the mesoblastic or primitive 

 segmentation (see a former paper before this Society, " The Post- 

 Embryonic Development of Julus terrestris" 1888). This renders it 

 probable that they are not a primitive development, but a recent 

 modification, agreeing with the fact that all other Myriapods breathe 

 by the more primitive method of tracheee. 



This mode of respiration differs from that in other Myriapods in 

 the following particulars : 



1. The tubes are collected into one definite organ, instead of being 

 distributed about the body. 



2. The tubes have no spiral thread. 



3. In acting on the blood just before it returns to the heart, so that 

 aerated blood is distributed instead of unaerated. 



It resembles the tracheae of other Myriapods in the following par- 

 ticulars : 



1. In the air sac into which the tubes open. 



2. In the cylindrical form of the tubes. 



3. In the branching of the tubes. 



The organs resemble the tracheal lungs of Spiders 



1. In the large air sac. 



2. In the number of tubes opening into an air sac. 



3. In the arrangement for bathing the tubes with blood in a blood 

 sinus. 



4. In the supply of aerated blood by the heart. 

 They differ from them in 



1. The form of the tubes, which in Scutigera are cylindrical. 



2. In the absence of the membrane which in Spiders surrounds 

 the organ. 



I therefore hold that the respiratory organ in Scutigefa holds a 

 position intermediate between the tracheae of Myriapods and the lungs 

 of Spiders. I hold with A. Leuckart (' Zeitsch. f iir Wiss. Zool.,' 

 vol. 1, p. 246, 1849, " Ueber den Bau und Bedeutung der sbg. Lungen 

 bei den Arachnidon") that the tracheae have developed into the Jungs of 

 Spiders and Scorpions, and I think that the organs in question form 

 a series of which the lowest term is the trachea?, the next the organ 

 of Scutigera, then the lungs of Spiders, and then of Scorpions. 



