Jan., 1906.] Occurrence of Sex Organs in Aelosoma. 435 



method of treatment and philosophy, geography in its higher 

 phases is a university subject. Universities in France, Germany, 

 Austria and to some extent in other countries, have prepared for 

 the studv of geography in their courses. Two or three Amer- 

 ican universities give some systematic instruction in advanced 

 geographv. Many more should and, I trust, will, if for no other 

 reason than the utilitarian, the preparation of teachers for 

 elementary and secondary schools and the equipment of men 

 for business, diplomatic, and government positions where a 

 knowledge of the principles of geography is of inestimable value. 

 To stim up, then, physiography and geography are two dis- 

 tinct sciences. They each contribute to the full appreciation of 

 the other ; especially does the former minister to the latter. They 

 often deal with the same basal materials, but not in the same way 

 nor to the same end. Physiography describes and classifies 

 phvsiographic features and discusses the processes and agencies 

 bv which thev are made. Geography shows the relations exist- 

 ing between man and his phA^sical environment and classifies 

 the influences and responses. Both physiography and geogra- 

 phv are large, complex, and, as yet, not fully developed sciences, 

 and therefore present to the investigator many unsolved and 

 difficult problems. 



A NOTE ON THE OCCURRENCE OF SEX ORGANS IN 



AELOSOMA.' 



Jas. a. Nelson, Ph. D. 



The genus Aelosoma, representing the family Aphanoneura, 

 and containing the most primitive members of the oligochaetous 

 annelids, is remarkable, among other things, in that sexual 

 reproduction occurs very rarely, the asexual method being the 

 usual one. The latter consists in a process of fission or budding, 

 by which the young individual is constricted ofT from the pos- 

 terior portion of the parent, this process often taking place so 

 rapidly that chains of individuals are formed, representing three 

 or more generations. This process is continuous during the life 

 of the individual, and probably amply suffices, as far as numbers 

 are concerned, to insure the maintenance of the species. Sexual 

 reproduction does, however, step in occasionally, and has been 

 described by U'Ddekem in 1862,- and more recently by Stole'' 

 and Maggi.'* According to these authors a testis is found in the 

 fifth segment, (counting the prostomium as the first) ; an ovary 



1 Cijntribvited from the Laboratory of Entomology and General Invertebrate Zoology 

 of Cornell University. 



2 Bull. Acad. Sci. Rov. Belg. XII. 



3 SB. Bohm. Gesc. 1889. 



4 Soc. Ital. Nat. Sci. I. 



