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body else very much distended. The contents of the stomach 

 are mostly unaltered yolk globules, but some of them hâve now 

 been decomposed and ccmminuted. The larva swallows and 

 swallows. increasing in size until it has reached its maximal size 

 at 1,24 mm, mostly resembling a mère bean or egg, the body 

 wall being enormously distended so as to form a very thin mem- 

 brane, even the head cône cannot be distinguished any more 

 extericrly, only in cuts (fig. 3 F). Now at length the yolk will 

 be digested, the imaginai dises are formed, and pupatien takes 

 place, during which the excréments are deposited in the host 

 egg as whitish masses between the pupae. 



The whcle developmental process takes place in the course 

 of 11-15 days, of which only few days are taken up by the first 

 stages before the regular bean-form in its maximal size is esta- 

 blished. The pupal stage lasts 10-13 days. 



Enock has recorded that the copula takes place as early as 

 in the host (Dytiscid) egg before the Prestwichias hâve hatched 

 from this; he déclares that in ail the parasitized Dytiscid eggs 

 feund by him (about 12) he has seen I cr more pairs in copula. 

 Also RlMSKY-KoRSAKOW confirms this statement as rie déclares 

 to hâve seen through the egg shell the copulation which will 

 last 10-15 seconds, and seen that one maie can fecundate ail 

 the females in the same egg little by little, if he is the only one 

 présent. Upon the whole the imagines in the host egg are said 

 by RlMSKY-KoRSAKOW to be very agile and vivaceour . 



This does net agrée with my observations which do, on the 

 other hand, agrée with those of HEYMONS. In the great material 

 which I had at my disposai (of brevipennis) 1 never saw any 

 copulation take place in the host egg, on the contrary ail ima- 

 gines will lie quite motionless until at last one lying next to the 

 shell will gnaw a hole in it and escape, then after a while the 

 spécimen which is now next to the hole— and only tha one — 

 will move, turn round and escape, and thus one by one will 

 successively awake to activity, surely because oxygen from the 

 water will more and more penetrate into the egg from the hole. 

 As HEYMONS states we can scarcely believe that a process as 

 copulation which surely must cause an increased consumption 

 of oxygen should take place in the thick-shelled and oxygen- 

 poor host-egg. ENOCK and RlMSKY-KoRSAKOW as well as Hey- 

 MONS and I are quite sure of having observed exactly, but it 

 passes my understadig how so widely differing observations 

 can be made. 



