CXXl 
their form and elasticity, to vibrate in a period corresponding to the 
exciting sound. 
I must confess, however, that they appear to me very ill adapted 
for any such function, and I am disposed to regard them, not as hairs, 
but as modified nerve-terminations, corresponding to the rods in the 
eye of insects. 
The fourth number of the sixteenth volume of the same journal is 
entirely composed of a very admirable paper by M. E. Mecznikow. 
This young naturalist, already one of our most zealous observers, 
promises to take a high rank among biologists, and the memoirs 
which he has already produced justify us in expecting great things 
from him. In the present memoir, after some introductory obserya- 
tions, he describes the development, first of Simulia, secondly of 
Miastor, thirdly of Corixa, fourthly of Aphis rosz, and lastly of Coccus 
(Aspidiotus) nerii. 
Both in the viviparous Cecidomyia and in Aphis M. Mecznikow 
has satisfied himself that the germinal vesicle divides and subdivides 
itself, the cells thus formed arranging themselves in a layer around 
the yolk, and thus forming the blastoderm. M. Weissmann, on the 
contrary, maintained that the blastodermic cells arose independently 
in the outer layer of the yolk: M. Mecznikow’s statement is, however, 
most probable in itself, and is fully corroborated by his figure, the 
accuracy of which there is no reason to doubt. It is true that he did 
not actually see the division take place either in Cecidomyia or in 
Aphis. He relies on the absolute similarity of the first two cells with 
the germinal vesicles, and their unlikeness to anything else in the 
eggs secondly, on their absence as long as the seminal vesicle is 
present, and their presence as soon as it has disappeared. I must, 
however, confess that I have never found in any insect egg any trace 
of this process, nor was Prof. Huxley more fortunate. Moreover, 
according to Leuckart, the blastodermic cells in Aphis arise suc- 
cessively not by division of, but by budding from, the germinal 
vesicle. As soon as the blastodermic cells have arranged themselves 
round the yolk, the hindmost of them increases in size, becomes 
darkened by granular contents, and thus forms a “pole-cell” or 
“ directive vesicle,” similar to those which have been observed in so 
many animals that we may almost regard their presence as general 
at this stage throughout the animal kingdom. 
Q 
