ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



207 



formed by the reunion of the two lateral ones, that is, toward the 

 anterior part of the head. The median stream which is, of course, 

 more ventral in position than the six others, enters the middle of 

 the labium, and passes along the dorsal half of that organ until it 

 nearly reaches the bases of the labial palpi. Here the stream turns 

 back laterally and ventrally, so that the returning current is along 

 the ventral half and in both lateral portions of the labium. Each of 

 the two streams of blood next toward the dorsum from the one which 

 supplies the labium, enters the outer side of a maxilla, flows along the 

 outer side nearly to the distal end of the basal joint of the maxilla, 

 and returns along the inner side of the joint to the head. The two 

 streams next in order, as the dorsal side of the head is approached, 

 are those that supply blood to the mandibles. Each enters the 

 mandible on its inner side, flows nearly to its tip, and returns on 

 its outer side. Dorsally to the currents supplying the mandibles are 

 those that flow into the antennae, which, in the larvae of Hydrophilus, 

 are used as trophi. Each stream enters 

 its antenna on the inner side, flows to 

 the distal end of the basal joint, and 

 returns on the outer side of that joint 

 to the head. After their return to the 

 head, the currents from the antennae 

 and trophi are lost among the muscles 

 of the head. 



Fig. 35 gives a more readily com- 

 prehensible idea of the direction and 

 extent of the streams. To complete the 

 figure one should imagine a stream of 

 blood toward the head, beneath the 

 arrow in the middle of the labium ; 



that is, with the head in the position larva of Hydrophilus ? piceus. 



Fig. 35. 



Dorsal view of head of young 



indicated in the figure, the Microscope Direction of blood-currents in the 

 can be focussed first on a stream appendages indicated by arrows. 

 flowing outward in the labium, and ItL'Z^or^St^trtT- 

 then with the fine adjustment, the tube tenna ; m, mandible ; ma, maxilla ; 

 can be lowered until a return stream I, labium, x 20. 

 toward the head is brought into focus. 



The currents of blood in the head are not indicated, as they would 

 too greatly complicate the figure. 



As the currents are not, of course, confined in arteries and veins, 

 as in vertebrates, the terms streams and currents of blood are used. 

 These streams occupy nearly the whole interior cavity of the 

 appendages in the larvae, the outward and return currents being 

 separated by partitions, of apparently a porous nature, which are 

 represented in the figure by dotted lines. These partitions, like 

 those described by Carus * in the abdominal appendages of the larvge 

 of Agrion jpuella, are very delicate, and extend, in the antennae, 

 mandibles, and maxillae, from the upper to the lower chitinous walls. 

 In no case have corpuscles of blood been observed to pass through 



* Carus, C. G., ' Bntdeckung eines einfachen vom Herzen aus beschleunigten 

 Blutkreislaufes in den Larven netzfliiglioher Insecten.' Leipzig, 1827. 



