174 [July, 



perfect cases are of all sizes, from very tiny ones of barely more than : 



one line's length up to the full measurement of three lines. The j 



cases are at first white and semitransparent, and so like miniature ; 



cases of ccespititiella in their early stage, that we may conclude they : 

 are formed in much the same way, but they soon get strengthened by 

 the stiffening material, and acquire a slight ochreous or buff tint. 



Specimens, both large and small, will often be noticed having a I 



white margin to the valves of the anal end, and a seam of the same i 



colour the whole way down the centre of the under-side, indicating , 



that the case has recently been enlarged, for these white portions are j 



the lines upon which the growth of the case takes place. Increased \ 



length is obtained by simple additions to the tail end, but to provide I 



for greater width the larva cuts open the case along the ventral side J 



from end to end, and then having added the necessary increment, ' 



closes it up again, though probably in the actual performance the \ 



addition and the closure are practically one and the same act. I was , 



once so fortunate as to catch a larva just as it had slit the case open j 



in this way, and on other occasions I have dropj)ed upon it at different I 



stages in the process of closing it up again, these only differing by the ; 



amount of cross-spinning that had taken place. \ 



I have reserved the consideration of their anatomy to the last. 



The figures represent the ventral portion of the 8th segment, with the ■ 



genital aperture in the female of each of the five species. In the i 



Lepidoptera, and still more in some other classes of insects, we have I 



long learnt to take advantage of the curious fact, that great structural j 



differences in the terminal segments of the male are often found to I 



occur in species otherwise extremely alike, but perhaps the attempt \ 



has seldom before been made to show, that in the corresponding parts | 



of the other sex also we may readily obtain, without any complicated i 



dissection, excellent and trustworthy characters, where the ordinary i 



superficial ones are barely sufiicient for our purpose. How far a , 



thorough study of these parts might repay the systematist it would be \ 



difficult to say, but that the chief gain would be in the discrimination j 



of species rather than in the arrangement of genera and families is I 



perhaps to be expected, when the extreme readiness of the parts to i 



change their form and their extravagant manner of doing it are taken ; 



into consideration. ; 



Looking at the figures it will be noticed that the outline of the l 



outer end of the ventral plate is much alike in sylvaticella, aUicolella ! 



and murinipennella. There is a deep smooth cut notch in the centre, j 



