— 29 — 



It is characteristic of Prestwichia that much more femaies than 

 maies are présent. RlMSKY-KcRSAKOW maintains that the dif- 

 férences in number is no': great (when three parasites are found 

 in cne egg 1 will appear to be a maie and two femaies, and 

 when only t°o parasites are found often one will appear to be a 

 maie and cne a female), but I hâve found in my materiai that 

 the femaies exceed the maies very much in number, in a certain 

 maerial reared from Agabus-eggs I thus ad 75 femaies and 

 only 4 maies, which corresponds with the rearings of ENOCK. 

 Thèse dirfering numbers surely mean that most of the femaies 

 will breed parthenogenetically (as in Rhodites rosae where, 

 according to ADLER, maies are decreasing and parthenogenesis 

 becoming a rule) and this I can ccnfirm, as newly ha.ched 

 femaies hâve oviposited without any copulation in Agabus — 

 eggs given them, and larvae hâve been develcped within them 

 (I need not say that I was o^ite sure that the Agabus-eggs used 

 had not been infested before). Also RlMSKY-KoRSAKOW states 

 that parthenogenesis takes place, but, according to him, the 

 unfecundated eggs will become maies, and the fecundated 

 femaies. He main:ains that maies originate in eggs depcsited 

 by a female in a host egg in which ne maie was présent and 

 thus without any possibility for copulation (as mentioned before 

 RlMSKY-KoRSAKOW says that copulation takes place in the host 



egg). 



My observations do not agrée with the above named. As said 

 I bred 75 femaies and 4 maies from a quantity cf Agabus-eggs, 

 and as 5-8 parasites develcp in each egg it may be understood 

 that in most of the eggs only femaies are présent and no maie. 

 I hâve bred more générations in continuity from Agabus-eggs 

 and always seen the fernales greatly surpassing the maies in 

 numbers, whereas if RlMSKY-KcRSAKOW was right, it should at 

 Iast hâve given about mère maies. Also in Odonate-eggs where 

 only cne parasite is reared from each egg, the surpassing num- 

 ber of femaies is maintained. 



On account of the short developmental time many générations 

 are established in a year, RlMSKY-KoRSAKOW states 4 in Northern 

 Russia, I cannot give any statement for Denmark, but 4 is surely 

 the smallest number hère. RlMSKY-KoRSAKOW mentions that in 

 Russia the Ist génération develops in the large eggs of Dytiscus, 

 found in May — June and the 3 other générations in eggs of 

 smaller Dytiscids found later on in the summer. My observa- 



