232 The American Naturalist. 



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Cross Fertilization and Sexual Rights and Lefts Among 

 Vertebrates.— The November number of this journal, page 1012, 

 under the title " Sexual Rights and Lefts," called attention to sexual 

 peculiarities I had recently discovered in certain Cyprinodonts. At 

 that time no satisfactory explanation of the purpose or origin of the 

 strange conditions offered itself. At present I would like to note in 

 these pages what upon further consideration appears to me the best 

 solution of the problem. Additional study has satisfied me that the 

 sexual conditions in the genus Anableps prevent close " inbreeding," 

 or, in other words, they secure cross fertilization. What in certain 

 plants is attained by means of short stamens with the long ones is in 

 these fishes realized by sinistral and dextral males and females. This 

 is a view in the case of Anableps that brings us in face of probable 

 benefit from the novel features, and of the possible causes of their evo- 

 lution. As bearing on the inception of the dextral and the sinistral 

 peculiarities we must consider the habit possessed by so many of these 

 fishes of swimming in pairs, side by side, a habit that induced Professor 

 Agassiz to name one of the genera Zygonectes, that is yoke swimmers. 

 The acquisition of more or less of a dextral or of a sinistral tendency 

 would not be at all unnatural in each of a pair habitually swimming 

 side by side in the same relative positions to one another. It may be 

 that cross fertilization will afford an explanation of conditions some- 

 what similar among molluscs. 



While writing of matters concerning the publication " The Cyprino- 

 donts," it should be mentioned, as kindly pointed out to me by Dr. A. 

 Smith Woodward of the British Museum, that the name of one of the 

 new genera, Glaridodon, was recently preoccupied among fossils, and 

 it may be well here to discard that name (p. 40) for the term Glari- 

 dichthys.—S. Gakman, Cambridge, Mass. 



Abnormal Sacrum in an Alligator.— Among a lot of young 

 alligators procured from New Orleans for the University of Chicago one 

 in which the skeleton was prepared, showed a very peculiar variation 

 in the pelvic region there being three instead of two sacral vertebras. 



There are as usual 24 presacral vertebrse. The 25th has the sacral 

 ribs inclined backwards and becoming slender. The 26th has strong 

 thick ribs, and the 27th, the first caudal in normal specimens, has also 

 well developed ribs articulating strongly with the ilium. The 27th is 

 seemingly biconvex. The first chevron is attached between the 28th and 

 29th and is, therefore, in the normal position as regards the serial num- 

 ber of the vertebrse, but is attached to the first vertebrse the last sacral 

 instead of the second. The whole pelvis has migrated backwards one 



