149 



<|iiite a different picture. The ventral reservoir is again shrivelled up lying only in 

 the first or two first abdominal segments and the blood has now arrived in t h<- 

 intestine; but also this is almost empty especially in its anterior part; in the 

 posterior part it contains a blood coagula of larger or smaller size. But round the 

 intestine, where formerly the fat body was, th*e whole body cavity is filled with 

 hexagonal figures, cross-sections of the ovaries with numerous eggs. Roughly spea- 

 king in the course of from eight to ten days the blood nourishment has been 

 transformed into eggs. If then in September we catch one of the C. lutescens-fe- 

 males, which, waiting for death, are sitting deep down in the grass covering the dried 

 ponds where they were hatched in spring, and where they have now laid their eggs, 

 and we now take cross-sections of the abdomen, we shall again get another picture. 

 The intestine is empty, but so also is the abdominal cavity round the intestine; 

 the ovaries are shrivelled up to two thin strings; the little mechanism has spent its force, 

 and is now only destined for one thing, to die and make room for another generation 

 now in preparation in the eggs slumbering in the dry mud under the withered grass. 



If we now investigate the case of another mosquito, hibernating not as egg 

 like 0. lutescens, hut as imago, like C. pipiens, we find an arrangement of quite 

 different sort. A cross-section of the abdomen of a C. pipiens in Sept., a few days 

 after it has left the pupa, shows a very thin intestine with strong folds of the wall. 

 a fat body with very small cells, strongly compressed; the sections further show 

 that the dorsal shields are much broader than the ventral ones, which on the other 

 hand are much more vaulted. A deep cleft is conspicuous laterally hetween the 

 dorsal and ventral shields. 



Already in the latter part of September the females of C. pipiens have found 

 their places of hibernation. If we now take one of these hibernating females from 

 my cellar, the cross-section gives quite a different result (Fig. 18a). The intestine is 

 as formerly extremely small, and in many of the sections difficult to find. On the other 

 hand the fat body is of quite different structure; the cells are much larger; between 

 them are large intercellular spaces, and the content of oil globules is enormous, 

 the cross-section of the abdomen further shows that this is now extremely extend- 

 ed ; the contour is circular; if we lay a hibernating mosquito from October in a 

 vessel with water and open the abdomen, enormous masses of oil glohules will 

 pour out; in a living animal we are able to see the oil globules with a lens through 

 the extended hody wall. In November — December the picture is quite the same: I 

 have got the impression, that the mosquitoes are at all events just as fat in Decem- 

 ber as they were in November. 



The question is now: What is the source of this fat? Most people would 

 probably say that it derives from the blood nourishment taken in by the females 

 before hibernation. This may be the case, hut I am not quite sure that this sup- 

 position is correct. Firstly I have never seen a mosquito with blood in its intestine 

 arriving at the hibernating places. Moreover, though in September I have very often 

 been silting in my garden, observing the swarms of dancing C. pipiens males, and 



