10 C. F. ROUSSELET ON THE SPECIFIC CHARACTERS 



the female of A. amphoi'a has two lateral humps, which are 

 very prominent in the young female, but become more or less 

 merged into the body cavity of older animals. 



In addition to the above characters, there are also specific 

 differences in the winter eggs in the three species. The winter or 

 ephippial egg of A. hrightwelli has been described as covered with 

 rounded, overlapping scales. There are no scales, however, the 

 appearance of scales being produced by large globular trans- 

 parent cells in the outer covering of the egg. In A. hrightwelli 

 the central yolk is yellow, and fills only one-half to two-thii*ds of" 

 the egg cavity, thus giving the appearance of a white cellular ring 

 all round. The outer shell envelope consists of a mass of large and 

 closely set globular, transparent, apparently empty cells of somewhat 

 varying size. The size of a measured winter egg was 204 /x. 



In A. amphora the yolk is whitish, fills the whole egg ca\aty ; 

 the outer shell envelope consists of numerous much smaller 

 globular transparent cells, through which a finely dotted inner 

 membrane can be seen. Size of egg, 170 //. 



In A. intermedia the whitish yolk fills about three-quarters of the 

 egg cavity ; the outer shell envelope is very thick, covered all over 

 with very minute dots, which appear to be the outer openings 

 of very fine tubes running through the egg-shell, for in optical 

 transverse section numerous fine parallel lines can be seen in 

 the substance of the egg-shell. On the surface there are a few 

 scattered globular transparent cells, and the general appearance 

 of this winter egg is quite difierent from the other two. The 

 size of the egg from one of the smaller specimens from Hertford 

 Heath is 136 /a. 



It will be seen from what I have said that A. intermedia is 

 really strangely intermediate in form and structure between 

 A. hrightwelli and A. amphora, and yet has characters of its 

 own, by means of which it can readily be distinguished ; it may 

 possibly have been produced by a crossing of these two species,, 

 but the characters are certainly constant at present. I have 

 found A. intermedia in various localities round London : Kew 

 Gardens, the canal near Hanwell, Hertford Heath, etc., and also 

 near Homburg, in Germany ; but it is certainly not so common 

 as A, hrightivelli. 



To recapitulate, the essential differences between the three 

 species named in this paper are as follows : — 



