476 Analytical Notices of Books. 
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 developement 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 antenne, upper joints of the legs, wings, &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 which 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 larve we perceive moreover, 
with perfect distinctness, that the currents passing through the branchie 
and upper joints of the legs, are merely outward arcuations of the late- 
ral descending streams. 
‘© *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 occtr at different 
periods of time in very different 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- 
+ This circumstance is illustrated by a diagram of the entire circulation ac- 
cording to the views of the learned authour. 
