10 THE CYPRINODONTS. 
less modification, in others; and in Heterandria, Glaridodon, and Girardinus, 
there are three. In addition, on the stays, lateral processes are prominent 
in some; while in others the inferior stay alone is to be discovered. On 
Xiphophorus there are four or five of the stays. Another feature of the 
modification occurs in the males of some species, of Glaridodon for example, 
in which the basal spines, to which the anterior anal rays are articulated, are 
much broadened. ‘This is most pronounced in forms on which the clasper is 
longest, and it furnishes a broader base of attachment for the muscles con- 
trolling the movements of the organ. 
By recent discussion attention has been directed to a decrease in the 
number of vertebra, of fishes in general, in and toward the torrid zone, and 
several theories have been propounded to account for the phenomenon. The 
species of this family, and others, have been somewhat carefully studied, — 
first, to determine the facts, and, second, to test the theories. It is found 
that those species making most use of the vertebra and the column have the 
greatest number of vertebrae whatever the temperature, as may be seen in 
the different genera together inhabiting Cuban waters, or those of Brazil, or 
in the different species of a single genus like Orestias in Lake Titicaca. It 
is true a decrease obtains, with few exceptions, in the direction of warmer 
waters, but warmth of water in such instances is attended by both increase 
in the amount of food and decrease in the need of it, thus lessening the 
comparative activity of the species. Some would ascribe the differences 
directly to natural selection. This hypothesis of course cannot be proved ; 
it begs the entire question. It is also found that with the decrease in the 
number of vertebra, there is in some cases a decrease in the number of fin 
rays and scales. 
The stomach is an enlargement of the intestine; it is not particularly 
distinct, and is without a pouch or caecal appendages. As with higher 
animals, the intestine is shorter in proportion to the greater amount of 
flesh in the food. Variation in regard to feeding habits in the species of 
a genus are readily indicated by comparisons of this organ. Fundulus in 
general has a comparatively short intestine; but in F. Kansae the tract is 
much elongated. Lebias has a medium length, while its nearest ally, 
Cyprinodon, has an intestine considerably longer. This organ in the mud- 
eating species is very long. 
A membranous air bladder is present in all the known species of this 
