324 W. WESCHE ON MALE ROTIFERS. 



swim in a straight line, and to or from the light. Thej are thus 

 brought up by the side of the trough and this is generally a 

 favourable moment for their capture with the pipette, and 

 transference to a compressorium for examination under higher 



powers. 



There is also another method of securing males, namely, to 

 watch for a female with the male egg. This is a comparatively 

 rare production, and is more circular in shape and smaller in size 

 than the female egg. When such a female Rotifer has been 

 secured, it can then be isolated in a live-box. In doing this it 

 will be necessary to give plenty of water, and see that the channel 

 round the edge is moist. To make assurance doubly sure, the 

 live-box may be placed under a bell-glass with some wet blotting 

 paper, or the hanging drop method, described in Mr. Karop's 

 useful and interesting paper which was read in March (see antCy 

 p. 265), might be resorted to. This isolation is not a very severe 

 trial of patience, as usually twenty-four hours is sufficient to 

 hatch out the male Rotifer. 



It is well known that Rotifers are parthenogenetic, and that 

 fecundation by the male is only necessary when the resting egg 

 is to be laid.* 



Maupas made some experiments,t and satisfied himself that he 

 could artificially bring about the production of male eggs by 



* The parthenogenetic egg has a smooth surface, and has much the 

 same appearance in all the species. The opposite is the case in the 

 resting egg. Thus : 



In Hydatina it is covered with hairs ; 



In Rhinojys a distinct morulation is seen, and the membrane has short 

 spined tubercles ; 



In Triarthra hrevispina it is markedly morulated ; 



In Metopidia solidus it is covered with short spines ; 



In Callidina plena it is sub-oblong in shape with a domed swelling at 

 the opposite extremities. This is given as a " resting " or " winter egg " 

 ('• winterei ") because of its close resemblance to those recorded by Dr. 

 Janson. Mr. Bryce, whose opinion carries very great weight, maintains 

 that it is not proved that " resting eggs " occur among any of the 

 Bdelloid Rotifera. 



t "Comptes Rendus, Ac. Sci.," 1890, p. 310. 



