DEVELOPMENT OF CYPRINUDONTS. 909 
stance where scales were ceveloped or where the fins had approximated their adult con- 
dition so nearly as in this case. The only instance known to m3 at this writing whore a 
continous 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 Zygonectes are, or are not, derived from such a fold would be an inter- 
esting observation. A marked acceleration is also noticeable in the development of the 
brain, a study of which by means of sections, as compared with that of the adult, 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 when the shad, 
cod, mackerel, bonito, and many other fishes are from three to six weeks old. 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 discriminately, 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 most of them by that time have acquired mandibular, maxillary, 
or pharyngeal teeth or both. The Fish Commission 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 writer, has not been in vain, 
because, even though the fish is too small to be of any praciical value, it has taught us 
that where Nature has so effectually provided for the protection of the young fish she 
does not require one adult to produce as many embryos. In Zygonectes twenty-five to 
thirty young is perhaps the limit of production for a single female; in Apeltes, 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 of 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 exter- 
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 snch as could be developed by 
natural selection so as to favor the survival of the greatest number of embryos ? 
‘‘ 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 Zygonectes, would be useful as a general character, as 
suggested by Colonel Marshall McDonald, to whose unselfish, helpful interest I am 3 
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. 
