THE CIRCULATORY SYSTEM. 



15 



structure. Taken together they correspond more particularly with 

 the brain of the vertebrate animals, and their structural develop- 

 ment and complexity appears to be correlated with superior 

 intelligence, such characteristics being very strongly marked in the 

 Ants and other Hymenoptera. 



2. The ventral ganglia. These are, of course, very closely con- 

 nected with the ganglia of the head. They differ very greatly in 

 number in different insects and even in the larva and the perfect 

 insect of the same species, this difference being clue to the greater 

 or less amount of concentration. 



It is generally assumed that in the primitive insect each seg- 

 ment had a simple ganglion, but some of these, in the course of 

 the development of the orders, have become amalgamated. This 

 concentration is, as Dr. Sharp and others have pointed out, 

 "concomitant with a more forward position of the ganglia," and is 

 very evident in the ScARAB.EiDiE, in which, for the most part, there 

 are no ganglia at all situated in the abdomen, all the abdominal 

 ganglia being joined to the ganglia of the metathorax. This has 

 been regarded as one reason for assigning a high position in the 

 order to the Lamellicornia ; but this cannot be pressed, as the 

 LucANiuiE have six or seven ventral ganglia. The character, 

 however, serves strongly to emphasize the complete difference that 

 exists between the Lucanidte and Scarabtltdve. The question 

 of the composition of the ventral chain is an important one, as 

 it is now becoming more extensively used as a help towards 

 classification. 



3. An accessory sympathetic system (or systems). This links up 

 various organs of the body with the general nervous system, but 

 apparently not very much is known with regard to it, except in 

 isolated cases. The frontal ganglion, shown in fig. 7, is a starting- 

 point for one portion of this system, which is then connected with 

 the brain system, and extends to the proventriculus, the series 

 being known as the stomato-gastric system. 



The Circulatory System. 



The blood has no red corpuscles but contains pale amoeboid cells 

 corresponding to the white corpuscles (leucocytes) of the verte- 

 brates. The organ which answers to the heart, and which, 

 functionally only, may be regarded as a true heart, is a dorsal 

 vessel, consisting of a delicate, pulsating tube, situated above the 

 digestive canal and divided into several chambers, arranged longi- 

 tudinally and opening one into the other. These by their alter- 

 nate contraction and dilatation (which may easily be observed in 

 transparent larva?), distribute the blood through the so-called 

 blood-vessels, which soon open into the haunoccel or perivisceral 

 space. The dorsal vessel is nearly always closed behind, but 

 is open in front and is provided with apertures at the sides ; 



