561 



projections, like those in certain Echinoderm larvae. In all re- 

 spects the Actinotrocha is a true Cephahda. 



We will now, with Metschnikoff, follow the life-history of the 

 Actinotrocha. The earliest stage he observed was when the larva 

 had a transparent, ciliated body, with an umbrella-like expansion 

 on the head, covering the mouth region, while the end of the body 

 was truncated. The young at this stage was much like a Phoronis 

 larva. Soon four projections arise at the end of the body, and 

 twelve long, arm-like projections grow out by the time the larva 



When the larva is about to transform into the Sipunculus, the 

 end of the intestine bends up, opening outwards near the mouth. 

 The umbrella is gradually withdrawn into the mouth, so that 

 finally only a crown of short tooth-like projections surrounds the 

 mouth. Finally the whole umbrella disappears in the oesophagus, 

 is actually swallowed, while the arms on the end of the body 

 are absorbed and disappear, and the end of the intestine projects 

 far out from the body behind the mouth. By this time the Sipun- 

 culus form is clearly indicated, the body being long and slender 

 and the mouth surrounded by a crown of short tentacles, and the 

 anal opening is withdrawn within the head. The change from the 

 free-swimming larva to the sedentary worm is effected in a very 



The Sipunculus, then, so far as its history is known, passes 

 through a Cephalula stage before transforming into the adult 



X. ANNUL AT A. 

 The life-history of Balanoglossus, a peculiar worm found in fine 

 sand along our whole coast from Cape Ann to Beaufort, North 

 Carolina, is one of singular interest. Its free swimming larva was 

 regarded by Muller, who discovered and called it Tornaria, as the 

 young of some starfish. Later studies by eminent naturalists only 

 seemed to confirm this opinion, until in 1869 Metschnikoff sug- 

 gested that it might be the larva of the worm, first .k^ribed 

 * under the name of Balanoglossus, or whale's tongue, by Delle 



AMER. NATURALIST, VOL. IX. 36 



