§ I 



OVIPOSITOR TEST 



The ovipositor is measured in so-called "anal fin units" 

 (A.U. ). One A.U. corresponds to one-eighth part of the 

 foremost radius of the extended anal fin (Fig. i). We use 

 small aquaria of 750 ml capacity, in which there are three 

 fishes, distinguishable from each other by their respective 

 sizes. These small aquaria are placed inside a larger one serving 

 as thermostat, and in which an optimal temperature of 22° C 

 is maintained (Fig. 2). The small aquaria are well aerated. 



/ adhesive 



2 iron bar suspending 



3 rubber tubings 



4 air -cock 



5 aquarium -frame 



6 iron bar 



7 small aquaria confain/ng the fishes 

 6 wall of the thermostat 



9 thermometer 



10 water of the thermostat 



Fig. 2. Front and side views of the testing equipment. 



When measurements are taken (every hour or two), the 

 small aquaria are removed from the thermostat and held up 

 to the light for a few moments, when it is possible to estimate 

 the length in A.U. of the ovipositor by eye and with suf- 

 ficient accuracy. 



When new fishes are used, and transferred from the cold 

 water to that at 22° C, there is an autonomous growth of 

 a few A.U. The first reaction to a steroid hormone, more- 

 over, is generally too low. For this reason we first sensitize 

 the fishes by causing them to react to the urine of pregnant 

 women (3 ml per 750 ml water). After i 2 to 14 hours the 

 ovipositors of the majority of the fishes have grown marked- 

 ly. Fishes that have reacted insufficiently are eliminated. The 



