132 The Philippine Journal of Science 1917 



As development advances, the ovarian follicles become highly vascular, 

 increase in size, and fill with a transparent fluid in which the embryo is 

 constantly bathed. This fluid is aerated by follicular circulation. The gills 

 of the developing embryo become functional comparatively early. During 

 the later stages of the intro-ovarian life, rythmatical breathing movements 

 of the embryo can be observed. 



The young are born in an advanced stage of development and show nearly 

 all of the diagnostic characters of the species. They undergo no marked 

 metamorphic changes after birth. 



RATE OF GROWTH AND FEEDING HABITS OF THE MOSQUITO FISH 



The young fish when born is from 3 to 5 millimeters in length, 

 is very active, and begins to feed soon after leaving the mother. 



From the brood of 21 fish, previously mentioned as born 

 on December 8, 1915, two were selected and placed in balanced 

 aquaria. Each of these measured 5 millimeters at the time 

 and were 21 hours old. Ten very young mosquito larvse were 

 selected by means of a pipette and placed in each aquarium with 

 the young fish. I saw one of these fish, while less than a day 

 old, catch and eat 8 of these mosquito larvae in less than five 

 minutes. The next day 40 larvse were added to each aquarium. 

 The fish were not able to handle the adult larval mosquitoes 

 as yet, although one fish was observed to catch a big larva by its 

 head, the larvse being fully as long as the fish. There was a 

 fierce struggle in which the fish was thrown from side to side; 

 however, it hung on and in the end succeeding in killing the 

 larva. 



A careful count was made of all the mosquito larvse fed to 

 each of the young fish, a net being placed over the aquaria so 

 that should any of the mosquitoes become adult they could 

 not escaped. 



On February 8, 1916, exactly two months after their birth, 

 the fish were carefully measured. I was able to distinguish at 

 this time that one was a male and the other a female. The 

 male was 20 millimeters in length, the female was only 19 milli- 

 meters. The male had gained 15 millimeters and the female 

 but 14 millimeters during the first eight weeks of their life. 

 During this period the male ate 886 mosquito larvae ; the female 

 ate 825. 



Two weeks later, March 22, the male was 23 millimeters in 

 length and had eaten 1,663 mosquito larvse. The female was 26 

 millimeters in length and had eaten 1,547 mosquito larvae. 



When the fish were 10 weeks old, the male was placed in the 

 aquarium with the female. He at once copulated with her. 



