DEVELOPMENT OF CYPRINODONTS. 9C9 



etar ce where scales were developed or where the fins had approximated their adult con- 

 dition so nearly as in this case. The only instance known to me at this writing where a 

 continons dorsal and ventral median fin-fold is never developed, is in the case of 

 Syngnathus, where the caudal rays are developed before the dorsal ones. Whether the 

 unpaired fins of Zygoneetea are, or are not, derived from such a fold wonld be an inter- 

 esting observation. A marked acceleration is also noticeable in the development of the 

 brain, a stady of which by means of sections, as compared with that of the adnlt, has 

 furnished me with some valuable clues in following up the developments of Teleostean 

 genera. 



" To sum up, this fish begins an independent career as far developed as whea the shad, 

 «od, mackerel, bonito, and many other fishes are from three to six weeks o'd. By so 

 much he has the advantage over these types in the struggle for existence in that he is 

 ready to feed, to pursue his prey disoriminately, as soon as he is born, while the other 

 forms alluded to are comparatively helpless until some time after they have absorbed 

 their yelk sac, although mott of them by that time have acquired mandibular, maxillary, 

 or pharyngeal teeth or both. The Fish Ccmmission authorities need never be uneasy 

 about the fate of the top minnows ; they will take care of themselves ; their species is 

 sure of survival. But our study, it would seem to the wiiter, has not been in vain, 

 because, even though the fish is too small to be of any practical value, it has taught us 

 that where Nature has so effectually provided for the protection of (he young fish she 

 does not require one adnlt to produce as many embryos. In Zygoneotea twenty-five to 

 thirty young is perhaps the limit of production for a single female ; in Apeliea, or the 

 four-spined stickleback, the male of which is provided, according to my observations, 

 with a spinning apparatus, with which he fabricates a nest in which the young are 

 hatched and taken care of, the number of eggs is from fifteen to twenty. Contrasting' 

 these small numbers with 100,000 to 3,000,000, the number of ova easily matured in a 

 single season by a single female of many anadromous and marine species, which have 

 heavy, adhesive or floating eggs, it would appear that the quantities of germs produced 

 by different species of fishes is in some way proportioned to their chances of survival. 

 Otherwise we are at a loss to explain the enormous fertility cf many marine forms ; the 

 astounding fertility of the oyster and clams is another instance illustrating this princi- 

 ple, where ova are matured by the tens of millions and where barely one out of a million 

 survives so as to attain adult age. 



"Certain adaptations of structure are also plainly noticeable on a comparative study of 

 fish ova. Thus the egg membrane of floating eggs is extremely thin, thinner than that 

 of heavy or adhesive eggs, while the thickest membranes are those provided with eter- 

 nal filamentous appendages. The most thinly clad hatch out soonest. May it not be 

 -that the thinness of the envelope, of the egg has some relation to the rapidity with 

 which the oxygenation of the egg is effected and consequently with the rapidity of tis- 

 sue and embryonic changes ? And, finally, who would undertake to say that all of 

 these modifications of the embryonic envelope are not such as could be developed by 

 natural selection so as to favor the survival of the greatest number of embryos 1 



" Before closing I wish to state that it is the oviduct of the female in some cyprinodonts 

 that is prolonged into a tube at the anterior edge of the anal fin, as I have lately learned. 

 This difference, as compared with Zygoneetes, would be useful as a general character, as 

 suggested by Colonel Marshall McDonald, to whose unselfish, helpful interest I am 

 deeply indebted for assistance in manifold ways while the investigation of the material 

 was in progress upon which the foregoing account is based. — Forest and Stream. 



