Life-history of Phalacrocera replicuta. 357 
from the connectives of the nerve-cord and unite in pairs 
to form ansee, or loops, from which lateral “ respiratory ”’ 
nerves usually proceed to the adjacent spiracles. We 
have not traced these nerves in the fly ; in the larva there 
are no thoracic spiracles. 
6. The reproductive organs of the larva. 
The ovaries (fig. 30) form a pair of cylindrical bodies, 
tapering to each end, which lie on either side of the 
beginning of the intestine. The ovary is invested by a 
thin fibrous sheath. It consists of a central cellular cord, 
which is excavated by a row of cavities, communicating 
with one another. ‘I'he wall is drawn out into many 
projecting follicles (fig. 31), which are pear-shaped, with 
narrow necks. Hach follicle encloses a group of large 
nucleated cells, one of which is probably selected to form 
an ovum, but this we have not seen. 
Such an ovary is unlike that of most Insects, and 
resembles, at least superficially, the ovary of many Mol- 
lusca, such as the cockles.* Instead of a small number 
of long ovarian tubes opening nearly at the same place 
into a common oviduct, we find in Phalacrocera a great 
number of short, single-chambered, though many-celled 
follicles, which open at various points into a central tube. 
The eggs of which (as we savpose) only one ripens in 
each follicle, may pass direct from such an ovary into the 
oviduct, whereas in the other arrangement they can only 
be liberated a few ata time. ‘The ovary of Phalacrocera 
seems to be adapted to the almost simultaneous discharge 
of all the eggs, while the more usual disposition is appro- 
priate to the successive discharge of eggs during a much 
longer time. In such Diptera as we are familiar with 
there is a multitude of short tubes or follicles, though 
Tachina and some few others have a few long tubes 
instead. 
The testes occupy the same position as the ovaries, but 
are much smaller (fig. 27). At first they are filled with 
closely packed nucleated cells (spermospores), which by 
division produce loosely packed spermatozoa (fig. 29). 
Ripe spermatozoa may be found in advanced larve. 
* Lacaze-Duthiers, Ann. Sci. Nat., Zool., 1854. 
