476 /Inalytual Notices of Boaksn 



in the primary state of the insect (that is to say in the embryo within the 

 egg) passes upwards towards the dorsal, and downwards towards the 

 ventral surface ; and may be regarded as analogous to the circulation in 

 the separate joints of Chara. 



" 9. The developemcnt or further evolution of this simple current 

 probably takes place in such a manner that, continuing in opposite 

 directions, the upper remains simple but has more dense canals, while 

 the lower subdivides into several currents, which remain for the most 

 part uncircumscribed by definite parietes. 



" *10. The currents of blood in all the external parts of insects are 

 directed from the head downwards, and it is therefore observed that in 

 the antenncE, upper joints of the legs, vpings, &c., the current of 

 blood through these parts, whether simple or branched, commences on 

 the side directed towards the head, and flows back on the side directed 

 towards the abdominal extremity ; an observation from w^hich alone, 

 but more especially when taken in connection with the absence of lateral 

 branches in the dorsal vessel (as demonstrated by anatomy), it results, 

 that they are all lateral arcuations outward and ramifications of the late- 

 rally retrogade currents. In transparent larva we perceive moreover, 

 with perfect distinctness, that the currents passing through the branchice 

 and upper joints of the legs, are merely outward arcuations of the late- 

 ral descending streams, f 



" *11. The form of the globules of the blood in insects is very 

 variable : they are larger or smaller, and sometimes appear to be entirely 

 wanting. But as they are the only means by which the current is ren- 

 dered visible under the microscope, it may be admitted that currents 

 sometimes exist where, under the microscope, none are to be seen. 



" *12. The currents of the blood in insects may occur at different 

 periods of time in very diflferent degrees of extension in one and the 

 same individual; with respect to which it needs only to be observed that 

 the more external they are, the more readily do they admit of suspen- 



f This circumstance is illustrated by a diagram of the entire circulation ac- 

 cording to the views of the learned authour. 



