22 THE NAUTILUS. 



forms which I can find to have been described from this region. 

 It is a more delicate and inflated species than either variabilis 

 C. B. Adams or vidleri Sowerby, if I am correct in my deter- 

 mination of these forms, and not ;i-t all close to either. It seems 

 to be nearest to the 0. harbarcims Dall, but the latter is much 

 more compact, more solid, and more highly tinted, as well as 

 usually of considerably smaller size. While it is possible that 

 the relatively thin callus on the lip is indicative of immaturity, 

 another large specimen which has come to my notice from the 

 San Pedro Channel agrees in this as in every other particular. 

 A figure will appear on a plate of this volume. 



THE CONJUGATION OF ARIOLIMAX CALIFOENICUS. 



BY HAEOLD HEATH. 



The newly hatched young of Ariolimax californicus measure 

 approxmnately five eighths of an inch in length, and under 

 favorable conditions become from three to three and a half 

 inches long at end of four months. Full-sized adults, measur- 

 ing in the neighborhood of eight inches, probably reach such 

 dimensions in not over ten months. A three-inch individual 

 possesses all of the essential features of the adult, though the 

 constitutent organs of the reproductive system are of small size. 



For several years the specimens of this species that are used 

 for class dissection at Stanford University have been collected 

 from a nearby and comparatively circumscribed area along the 

 San Francisquito creek where the conditions throughout are 

 uniform. It was therefore surprising to find that annually 

 fully five per cent of the large-sized animals dissected in the 

 classroom lacked the penis entirely, while in an equal number 

 it was abnormally undeveloped when compared with that of 

 smaller individuals which had not yet reached sexual maturity. 

 As the years went by the conviction became stronger that at 

 some previous time the penis in all such specimens had been 

 cast ofT, and that its diminutive proportions in otherwise fully 

 formed animals represented a regenerative stage. 



To test the correctness of the hypothesis fully two hundred 



