252 



SCIENCE. 



[N. S. Vol. XI. No. 268. 



remote from one another according to the 

 character and extent of the available bot- 

 tom. Spawning is intermittent and usually 

 covers a period of several hours. 



Notes on a Dakota Axolotl. H. L. Obboene. 

 A new Axolotl was found in March, 1899, 

 in Amenia, ISTorth Dakota, an occurrence 

 farther north than heretofore known. The 

 body proportions are those of an Amblystoma. 

 Its total length is 312 mm. It possesses the 

 following larval characters different from 

 previously known Axoloth : (a) a dorsal fin 

 beginning on the level of the second body 

 ring, 8 mm. high, running around the ab- 

 domen to the cloaca; (6) a smooth area of 

 the skin on each side of this in the dorsal 

 region ; (c) a skin beyond the smooth area 

 in the trunk region minutely warty-rough- 

 ened, and marked with scattered circular 

 dark spots ; (d) eyes located one-fifth of 

 the distance from the angle of the mouth to 

 the origin of the third gill ; (e) the longest 

 of the three gills as long as the head ; (/) 

 the gills all broadly spatulate and flattened 

 and the margin divided distally. Thefollow- 

 ing characters of the adult are present : (a) 

 all the four limbs are completely formed ; 

 (6) the lungs are fully developed ; (c) the 

 oviducts are much enlarged and filled with 

 eggs ready for deposition . Characters of the 

 skin, the size and form of the gills distin- 

 guish it from either the Mexican form or 

 from the Siredon lichenoides of Baird and 

 Girard from New Mexico. 



The degeneration of the eyes of the cave Sala- 

 manders. C. H. ElGENMANN. 



Will be published shortly in full in 

 Science. 



The arrangement of the single and twin cones in 

 the retina of fishes. C. H. Eigenmann. 

 "Will be published shortly in The Amer- 

 ican Naturalist. 



Notes on the Natural History of Polyodon. C. A. 



KOFOID. 



In the Illinois Eiver and its adjacent 

 waters, Polyodon is pelagic in habit. Its 

 food is typical plankton, chiefly Entomos- 

 traca and the larger Eotifera and Protozoa, 

 with no evident admixture of bottom rub- 

 bish or sedentary organisms. In swimming 

 the mouth is held wide open, without the 

 rhythmical respiratory movements common 

 in most fishes, though it is occasionally 

 closed energetically. The plankton is thus 

 strained from the water by the long gill- 

 rakers, and Polyodon is a living plankton 

 net. The fish was never observed to use the 

 bill to stir up the bottom or in any mechan- 

 ical way. It quickly perceives plankton or 

 ground fish added to the water of the tank, 

 and, when feeding, circles repeatedly over 

 the same path, at times dragging the lower 

 fins upon the bottom. The bill isabundantly 

 supplied with sensory structures and serves 

 as an expanded sense organ and not as a 

 mechanical aid in feeding. 



On Platydorina caudata. C. A. Kofoid. 



This new genus of the Volvocidae has 

 been found in the Mississippi, Illinois and 

 Wabash basins in summer and fall months. 

 It consists of a plate of 16 or 32 similar 

 biflagellate cells arranged in a horse-shoe 

 shaped ccenobium, which bears at its pos- 

 terior end 3 or 5 tails formed of the matrix 

 and sheath. The two faces are exactly 

 alike, alternate cells upon either face pre- 

 senting the flagella to the surface. The 

 plate is slightly twisted in a left spiral and 

 the rotation of the colony in locomotion is 

 predominantly from right over to left. The 

 polarity of this genus is the most pronounced 

 in the family being structural as well as 

 physiological. The two transverse axes 

 are also established though their poles are 

 not differentiated. Asexual development 

 is similar to that of Eudorina with a subse- 

 quent flattening of the ellipsoidal ccenobium 

 and an intercalation of the cells of the two 

 sides. Sexual development not known. 



