i] THE STRUCTURE OF CONVOLUTA 11 



coffensis from the following facts. Occasionally, 

 among just-hatched larvae specimens occur which 

 fail to respond like their fellows to gravitational 

 stimulus. Such specimens are found, on microscopic 

 examination, to lack properly developed otocysts. 

 For example, if numbers of C. roscoffensis larvse are 

 taken up with water into a glass tube and the tube 

 is shaken slightly, the animals come down, some 

 tumbling, some curvetting. These animals in general 

 respond to vibration by a geotactic movement that 

 is, one having reference to the line of action of 

 gravity but the one or two, devoid of otocysts, fail 

 to descend, remain glued to the side of the tube and 

 are dislodged with the greatest difficulty. 



As indicated already, the bodies of Convoluta 

 possess a well-developed system of muscles by the 

 ordered contractions of which the movements of the 

 animals are effected. 



The digestive system is of a primitive order. A 

 well-developed mouth, capable of a wide gape, occurs 

 on the under sl3e of the body rather nearer the 

 " head " than the " tail " end. The mouth communi- 

 cates by a short gullet, not with a distinct digestive 

 tube, but with a loose, central tissue. Hence food 

 which is ingested passes through the mouth to the 

 gullet whence it is distributed to improvised spaces 

 or vacuoles in the tissues (Fig. 3). In these vacuoles 

 it is digested. The undigested residue is discharged 



