] 72 tJ"^^' 



In its simplest form the shell is symmetrical, the panels being alike 

 in form and size on the two sides, and its general shape more or less 

 cylindrical. This is its condition almost universally in ApMoclisefa, and 

 several excellent illustrations of it have already been given in 

 Mr. Collin's figures. But when we turn to Phora we find that this 

 symmetry is for the most part lost, and while the right panel remains 

 the simple structui'e it is in Aphiochseta, the left one is fissured trans- 

 versely and sometimes much crumpled at the same time. The fissure 

 may extend only a comparatively short way across the panel as in 

 urhana {vide fig. 4), but usually is so extensive as to leave a mere strip, 

 so narrow, that unless the hypopygium be fully exposed or be dissected 

 out, the panel appears to be cut completely in two. In the j^cretinis 

 and Inqvhris group the hind corner of each panel is prolonged into a 

 flap, which is usually of equal length on the two sides, or one may be 

 longer than the other as in vitrea {vide fig. 1). In vnispinosa and its 

 allies the saddle is very short and the panels are long, narrow and 

 depending flaps, and the ventral plate correspondingly large. In the 

 conciniia and ahdominalis group (figs. 2 and 3) the distinguishing 

 feature is the very long anal organ ; the subanal body is concealed, 

 the panels are very large and of equal size, though the left one is deeply 

 fissured. Still further modifications arise in the urhana — hergenstammi 

 (domestica) group (figs. 4 and 5). In the first place the hypopygium 

 loses its more or less cylindrical shape and becomes globular and is 

 usually very large ; moreover it no longer forms a closed chamber, but 

 leaves the subanal body exposed. The right panel is large and simple 

 as usual, but the left one is always somewhat rediiced in size, and in 

 urhana and its allies fissured also, but in hergenstammi and erythronota 

 merely reduced, whilst between it and the ventral plate is a large 

 triangular piece {b in the figures) which I believe to be part of the 

 subanal body. On the right side, projecting beyond the large simple 

 panel, is a long slender process {d) which generally looks as if it 

 belonged to the panel, but under favourable conditions is seen to come 

 from underneath it, and must also be part of the subanal body. 



Hypocera. Here we ai-e met with a very remarkable departure 

 from the common type. In Apkiochaeta and Phora the anal organ 

 invariably finds an exit by issuing from underneath the saddle. In 

 Hypocera it does so by piercing the saddle itself. In some cases {cari- 

 7iifrons and femorata) the exit is flush with the general surface, so that 

 an anal organ in the sense of a projecting l)ody cannot be said to exist, 

 but in others an organ is present of the short papilla-like form so 

 commonly found in Phora. Among the British species citreiformis 



