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SCIENCE 



[N. S. Vol. XXXVI. No. 920 



proposed for it the generic name of Gyro- 

 coccus, and owiBg to the striking flaccidity 

 of caterpillars dying as a result of its pres- 

 ence, we have selected the specific name flac- 

 cidifex. 



A much more detailed account of our work 

 will be published later. 



R. W. Glaser, 

 J. W. Chapman 

 BussET Institution, 

 Forest Hills, Mass., 

 July 22, 1912 



THE PROLIFICNESS OF GAMBUSIA 



On June 3, 1912, there was received at the 

 aquarium of the Bureau of Fisheries in Wash- 

 ington a lot of top minnows ( Gamhusia affinis') 

 from the lower Potomac River, comprising 

 several males and about 90 females heavy 

 with young. On June 7, the expulsion of the 

 young began, and by June 27 all the females 

 had become spent. 



The viviparity, the relative scarcity of 

 males, the great disparity in the size of the 

 sexes and various other facts regarding this 

 species are well known, although I have been 

 able to find no adequate account of some of 

 the most interesting phases of its life history. 

 The principal object of this note is to call at- 

 tention to the remarkable prolificacy of this 

 little fish, which probably has few parallels 

 among viviparous vertebrates. 



The young are expelled in lots of 1 to 5 at 

 short intervals, and the entire brood is de- 

 livered in the course of one and a half to three 

 hours. The young swim readily and actively 

 immediately after expulsion. Their length at 

 birth is 8 to 9 mm. The progeny of one 

 mother fish forms a very sizable school; and 

 it was this that suggested the taking of an 

 accurate family ecnsus. On one moribund 

 fish 5 cm. long, that had apparently succumbed 

 from inability to expel her young, a Cesarian 

 operation was performed, and 33 living and 

 51 dead embryos were taken. Other fish 4.5 

 to 5 cm. long were killed, and counts of the 

 fully developed young were made, the numbers 

 ranging from 85 to 134, the average for all 

 fish examined being exactly 100. 



The production of two broods in a season 

 has been suggested by the fact that young are 

 born in spring and also in late summer. This 

 may indicate only a protracted breeding sea- 

 son; but in the fish now under observation 

 there are conspicuous ova which might easily 

 reach full development in six to eight weeks, 

 and fish from the same locality which I ex- 

 amined 22 years ago contained large embryos 

 on August 11. If there are later broods, as 

 I am now inclined to believe, this might ac- 

 count for the marked difference in the aver- 

 age number of young ascertained to be pro- 

 duced by fish observed in June, 1912, and by 

 fish of same size and from same stream in 

 August, 1890, the average for the former 

 being 100 and for the latter 24 (the extremes 

 being 18 and 30). Inasmuch as a second lot 

 of ova would have to attain a certain degree 

 of development while the abdomen was 

 crowded with embryos, it might easily happen 

 that fewer eggs would come to maturity and 

 be fertilized than in the case of the first brood. 

 This may afford a clue to the statement of the 

 late Professor Ryder that " viviparous forms 

 like the cyprinodonts have comparatively few 

 ova, and the number may be as few as 15 or 

 20 in such a form as Gamhusia." ' 



An interesting observation is the canniba- 

 listic tendency of the parent fish. Notwith- 

 standing other food was present, the adults 

 showed a pronounced fondness for their off- 

 spring, and began to feed on them soon after 

 they were bom. In order to save the young, 

 it was necessary to retain the adults in a wire 

 cage through the meshes of which the young 

 could escape into the aquarium. One fish 

 4.8 cm. which was transferred to a special re- 

 ceptacle produced 85 living, healthy young, 

 and devoured about half of them during the 

 second night. Another fish that was under 

 observation chased assiduously her first bom 

 as soon as it was expelled. 



H. M. Smith 



Washington, D. C, 

 July 1, 1912 



' Bull. U. S. Fish Comm., 1883, p. 196. 



