§ I 



SEXUAL CYCLE OF RHODEUS AMARUS ? 



the entire time of spawning, oviposition occurs only twice; 

 in most cases it occurs 4 to 5 or even 7 times. It appears 

 from the curves that the ovipositor grows periodically, in 

 periods of, generally, 6 — 8 days; sometimes, however, there 

 may be periods of from 11 — 13 days. It is possible that, 

 in these fishes, an ovulation-phase is missed. It is further 

 remarkable that the growth of the ovipositor takes place in 

 two stages. The lengthening from o — 5 A.U. may take 

 weeks; the lengthening from 5 A.U. to the complete length 

 occurs very quickly — usually within 24 hours. Shortening 

 after oviposition also takes place rapidly, the starting length 

 of about 5 A.U. generally being reached again within 24 

 hours. During the spawning period, however, the length of 

 the ovipositor is never reduced to o A.U. During this period it 

 fluctuates between 5 and 8 A.U., reaching a top oviposition 

 occurring at intervals of about a week. 



When we analyse the different stages of ovipositor growth 

 during spawning time we distinguish the following (Fig. 



79):- 



A.U. 



1-infi/tration phase 



2=inc/mation 



2=defiltration 



4. 



2 4 6 8 10 12 



' ii 20 22\ '^J I 28 30 32 'p4 36 38 



j 3'^sfage: 

 { 2"''stage: \ reduction 



1^* stage: growth period, \disposition period period. 



Fig. 79. Analysis of the different stages of ovipositor growth during 

 spawning time. 



ist Stage. Length o — 5 A.U. The ovipositor is in the grow- 

 ing period. Histologically, this phase is characterized, at any 

 rate under experimental conditions, by numerous mitoses. 

 2nd stage. Length 5 — 24 A.U. The ovipositor is now at 

 the laying stage. It is periodically able to attain rapidly a 

 maximum-length, rendering egg deposition possible. The 

 following phases may be distinguished;— 



