ANATOMICAL STRUCTURE OF KERRIA. 293 



tribution, others are confined to certain ponds and 

 marshes or even to certain spots in these ponds. Some 

 ponds contain absolutely no oligochseta of interest, others 

 swarm with common forms, others again may contain 

 a few endemic species for which we search in vain 

 somewhere else. Around San Francisco each one of 

 the few ponds in the region contain endemic forms, 

 while other species are common in them all. I found 

 the same to be the case in Mexico and Central America 

 as well as in the Sierra Nevada of California where, even 

 in the high mountains where water in the form of springs, 

 creeks and rivers form a perfect system and is found 

 everywhere, most interesting forms of oligochceta are 

 restricted to certain springs or swamps. The cause may 

 possibly be laid to the differences in the quality of the 

 water, which though slight may be sufficient to prevent 

 a wider and more general distribution of species. 



Kerria Beddard, 1892. 



Minute fresh water oligochgeta related to Ocnerodrilus 

 and Gordiodrilus. Spermathecal pores between somites 

 vii and viii and viii and ix. Spermiducal pore in xviii. Ovi- 

 duct in xiii. Oviducal pore in xiv. One pair of diverticula 

 of the oesophagus in ix containing parallel blood vessels 

 which do not anastomose. Salivary glands on the 

 pharynx. Septal glands surrounding the oesophagus 

 in somites v, vi, vii and viii. The posterior nephidia 

 covered with large peritoneal cells. No blood vessels 

 on the nephridia. The ventral and dorsal vessel con- 

 nected by two pair of hearts in somites x and xi. 

 No other connecting vessels. The prostates open in 

 somites xvii and xix. The sperm duct opening inde- 

 pendently in somite xviii. The prostates and sperm duct 

 open on two crescent-shaped zones, one on each side of 



2d Seb. Vol. III. ( 22) April 15, 1893. 



