Seal — Breeding Habits of Viviparous Fishes. 93 



Of course, normal action in fishes confined in aquaria is de- 

 pendent on a satisfactory environment — warmth, proper food, 

 etc. If conditions arc unfavorable and they are not comfortable 

 there will he no sexual demonstration. 



Prof. Ryder says further: ' The young, when born, are stated 

 by Mr. Duly to be about f of an inch in length and to be ex- 

 pelled in a single mass, consisting of 8 to 11 young fishes at a 

 single effort. This mass as soon as it escapes is seen to be 

 composed of the infant Gambusia, which at once separate and 

 move away. No membrane seemed to be expelled together 

 with the mass of young, so that it is probable that in this species, 

 as in Anableps and the Embiotocidse the foetuses rupture the 

 follicles in which they developed a short time before birth." 



One has only to open a gravid female to see that Mr. Duly's 

 account of the birth of Gambusia would be a physical im- 

 possibility. The ova of a full sized Gambusia are, when fully 

 developed, about an eighth of an inch in diameter, transparent 

 and non-adhesive. Each one is held, apparently, by a thread 

 of membrane to a central nucleus the character of which could 

 only be determined by microscopic examination. The young 

 fish can be seen fully formed, their eyes moving as they turn 

 around in the egg. They are expelled one at a time and the 

 ejection of each fish is so rapid that they appear as though shot 

 out with some force. This, however, might be due to the 

 bursting of the follicle and the uncoiling of the fish as it is 

 released from restraint. When they first appear they are still 

 in a somewhat curved form but they quickly straighten out and 

 swim into hiding. The follicles are undoubtedly ruptured at 

 the moment of extrusion, whether inside or out, 1 never suc- 

 ceeded in observing, but it appears the more probable that it is 

 inside. The young fish are already pigmented and altogether 

 unlike the generality of embryo fishes. Oviparous species, when 

 hatched, having an umbilical sac and being for some time 

 unable to feed and quite helpless. They are also transparent 

 and very delicate, while the young of the viviparous fishes are 

 apparently, except in size and the development of the male 

 sexual organ, as fully developed as the adult. I would say 

 that tV to i inch is nearer the size of the fish when born than 

 f inch, although the size, no doubt, varies with the size of the 

 female. The intervals between the extrusions vary from several 



