586 
MR. B. T. LOWNE ON THE MODIFICATIONS OF 
The rhabdia are less regular in size and structure than those of the Syrpliidse, as 
they intercommunicate with each other in the manner represented in fig. 15. The 
axial threads vary from four to twelve after the intercommunication of the rhabdia. 
r fhe communicating branches contain only two axial threads, and the rhabdia near the 
tetrasomes contain four axial threads (fig. 15a). I do not think the axial threads 
intercommunicate. Fig. 16 represents the rhabdia and axial threads in transverse 
section. 
Beside the pigmented monihform fibres of the rhabdia, which are like those in the 
eye of Syrphus, there is a network of stellate pigment cells between the rhabdia, 
which contain a brilliant rose-coloured pigment ; this becomes darker as the age 
of the insect advances. 
A quantity of granular orange-coloured pigment is collected at the inner extremity 
of each rhabdion in a small spherical mass (fig. 17). The inner extremities of the 
rhabdia seen in situ have the appearance of a layer of polygonal epithelium. 
Stomoxys calcitrans. — The only difference that I have been able to observe in the 
eyes of this insect as compared with those of Musca vomitorici is that the corneal 
facets are smaller : a condition which appertains in all small insects. They are only 
TliVoth of an inch in diameter. 
Tdbanus bovinus. — I have only examined the eye of Tabanus in dried specimens, 
so that I can only speak of the chitinous framework by which the various parts of 
the eye are supported. This attains a very remarkable development in Tabanus 
(figs. 18, 19, and 20). Not only are the chambers surrounded by chitinous hexagons, 
but the rhabdia are invested by chitin, and are connected by membranous septa, 
which divide the spaces from each other in which the trachea lie. These septa are 
strengthened by transverse thickenings. The most remarkable deviation from the 
ordinary structure of the dipterous eye is seen in the structure of the rhabdion, 
which appears to consist of two separate halves divided from each other by a fissure, 
each having its own sheath. I have found nothing like this in any other insect ; 
but the structure needs investigation in the recent insect. It is apparently identical 
with a condition described by Dr. Grenacher as existing in the rhabdia of some 
Coleoptera. * 
V. The Struct ure of the Eye in Agrion puella. (Figs. 21 to 24). 
In Agrion puella the type of the eye does not differ greatly from that in the 
Diptera. The chamber is much deeper and is filled with a gelatinous fluid. It is 
prismatic in form, and has a ring of four very transparent cells immediately Under 
the cornea (fig. 21a) ; but in AEschna there are from eight to twelve cells.! The 
walls of the chamber (fig. 21) are not surrounded by pigment cells, but sixteen are 
found around the tetrasome. Long, exceedingly fine processes are given off from 
* Lnc. ,n 
t .Claparede. 
