OBSERVATIONS ON MONOGENESIS IN 

 METRIDIUM. 



BY HARRY BEAL TORREY. 



CONTENTS. 



Page. 

 Plate XXI. 



I. Introduction 345 



II. Longitudinal Fission 347 



(a.) Equal , 347 



(b. ) Unequal 347 



[II. Basal Fragmentation 352 



I V. Budding 353 



(a.) Pedal : 353 



(b. ) (Esophageal. 354 



V. Colonies of Three and Four Individuals 356 



VI. Summary 357 



Bibliography 359 



Explanation of Plate 360 



I. Introduction. 



The material for this investigation was furnished by 

 Metridium fimbriatum Verrill, an extremely abundant spe- 

 cies in the harbor of Oakland, Cal. It is practically iden- 

 tical, according to Verrill, 1868, with M. marginatum of 

 the eastern coast, and M. dianthus of Europe; these three 

 species being distinguished without doubt solely on account 

 of their wide separation geographically. 



The animals were found crowded together in great num- 

 bers upon the piles supporting the two railroad bridges 

 which cross the estuary. They range as high as three feet 

 above mean low-water mark. The water is brackish, and 

 at ebb tide is exceedingly dirty. They are quite hardy and 

 may be kept indefinitely in aquaria. Several specimens 

 have been in captivity since October, 1897; yet they are 

 not so vigorous as they were in their natural environment. 

 The change in their conditions of life has probably served 

 to retard the processes of asexual reproduction described 

 hereafter. 



[345 J Oct. 20, 1898. 



