REPRODUCTION 



217 



fertilisation, and develop immediately ; they are often hatched 

 within the tube of the tubicolous species. 



Under certain conditions the unfertilised females produce 

 exclusively smaller eggs, which develop into males. Maupas 1 

 has demonstrated that a rise in temperature to a minimum of 

 26 C. (79 F.) is the efficient factor. But as Bergendal points out, 2 

 the critical temperature probably varies with the antecedent con- 

 ditions of the race, since males occur in Greenland at a very 



FIG. lU.-Diylena catdlinu. (After Weber.) A, Male ; B, the pair in copula ; 

 C, female. j>, Peuis ; te, testis. 



much lower temperature ; and it would seem probable that a 

 temperature approaching that at which the pools habitually dry 

 up is what is necessary for the production of males, as a provision 

 for those fertilised eggs, which, having a hard shell often adorned 

 with prickly prominences, and usually remaining for some time 

 before development, are capable of withstanding drought ; such 

 eggs are termed "winter eggs," but a better term would be 

 " resting eggs " (German, " Dauereier "). 



The male organs consist of a testis (Fig. 113, A, te} with acces- 

 sory glands, a large seminal vesicle, and a protrusible or project- 

 ing penis (_?;). In Notommuta and Diylena true intromission 



1 C'. 11. Ac. Set. cxi. 1890, \<. 310 ; cxiii. 1891, p. 388. 

 2 Ada Unit. LtuuL xxviii. 1891-92 



