THE CYPRINODONTS. 7 
ation, and in the shapes and sizes of their fins are undergone by males in the 
breeding season, for examples, in Mollienisia and Xiphophorus, the former in 
its enlarged and ornamented dorsal fin, the latter in its sword-shaped caudal, 
and both in the acquisition of brilliant colors over the body. By common 
experience collectors find males to be less numerous than females. The 
striking appearance of the male will no doubt be claimed as evidence of 
selection because of a possible benefit in enabling the female more readily 
to find him; it may also be utilized in explaining the discrepancy in num- 
bers since it must be effectual in making him an object of more prominence 
and a more frequent prey than the other sex for enemies of the species. 
From this one might be led to inquire whether the species is not on the way 
to extinction, or whether the females eventually are somehow to continue its 
existence on their own responsibility. 
Plates LX. to XII. show admirably, so far as black and white may do it, 
various phases of the coloration in species of several genera. These plates 
are from the pencil of the artist Sonrel; they were originally intended by 
Professor L. Agassiz for his work on the North American Fishes, of which the 
present is to be regarded as a continuation. The differences between the 
young stages, in which the sexes are alike, and the adult, in which males differ 
from females, of Fundulus majalis, are indicated on Plate IX. Very young 
individuals are blotched with black along the side ; adult males have vertical 
bands, while adult females are longitudinally banded, except at the base of the 
tail. On Plate X. variations within the species Zygonectes Nottii are shown 
to include all phases between such as exhibit a spot on each scale and those 
with longitudinal stripes or transverse bands or combinations of both bands 
and stripes. Plate XI. depicts, among the ordinary variations of form and 
coloration, a couple of the startling mixtures occasionally met with in Gam- 
busia Holbrookii, Fig. 4 and 5, in which the specimen takes on a dress entirely 
at variance with that common to the species. The presence of parasites in 
certain individuals thus peculiarly marked suggests a possible connection of 
such variation with disease. The Professor has figured both sexes of Mol- 
lienisia latipinna on Plate XII., and has indicated the progressive modifica- 
tion of the male. Ornate as shadow and light have made these figures, 
without considerable more assistance, the imagination will yet fail to sup- 
ply the tints, of blue, green, orange, silver and gold, necessary to represent 
the ornamentation of a living individual. : 
The most common form of body is slightly compressed; it varies to 
