THE MOVEMENTS OF THE ENTEROPNEUSTA 



AND THE MECHANISM BY WHICH THEY 



ARE ACCOMPLISHED. 



WM. E. RITTER. 



The observations upon which the present paper is based were 

 made, so far as they pertain to the living animal, upon two 

 species of the group found on the Coast of California and Wash- 

 ington. These are Balanoglossus occidentalis Ritter (MS.) and 

 Delichoglossus pusillus Ritter (MS.). The first mentioned is 

 abundant at Puget Sound, and is found, though in small num- 

 bers, at San Pedro, California. The second is widely distributed 

 along the Coast of California and is exceedingly abundant at San 

 Pedro, where it lives side by side with the first. 



My study of the movements have been made mostly on D. 

 pusillns. This small species is so abundant in limited areas at 

 San Pedro that a single shovelful of the sand in which it lives 

 may contain several dozen. Its place of greatest abundance is a 

 large sand flat, exposed at low tide, just inside the mouth of the 

 inner harbor at Timm's Point. The sand in which the animals 

 live is compact and homogeneous and contains much fine argil- 

 laceous material, the whole being blackened by decaying organic 

 matter. In some places the creature is found among the roots 

 of scattered patches of eel grass. Although the species is closely 

 related to D. Kowalevskii of the Atlantic Coast of the United 

 States, it is considerably smaller. It never produces the coiled 

 castings so characteristic of its eastern relative. In fact, I have 

 failed to discover any marking on the surface of the sand that 

 can be relied upon to reveal the presence of the creature. The 

 absence of the casts which are such a convenience to the collector 

 is, however, compensated by the animal's habit of the protrusion of 

 the proboscis from the ground. At low tide large numbers of the 

 orange-colored proboscises may be seen with the tips only, or 

 sometimes with nearly the entire organ, lying flaccid on the sand. 

 A slight jarring of the ground causes a prompt withdrawal of the 

 exposed part. Professor B. M. Davis, of the Los Angeles State 



2 55 



