»8 THURLOW C. NELSON 



rois' theory of the protective action of the dissolved style 

 substance. 



My own investigations of the embryological development of 

 the crystalline style were carried on during three summers on 

 the New Jersey coast, while engaged in a study of the food and 

 feeding habits of the veliger larvae of Ostrea and Venus. 



In the prodissoconch larva of Ostrea I find in the epithelium 

 of the stomach the same two regions, differing in the cilia they 

 bear, as were described by Drew for Nucula. Most of the 

 stomach wall, like that of the oesophagus, is covered with short, 

 even cilia which beat at a uniform rate. Just anterior to the 

 middle of the stomach, and situated on opposite walls, are two 

 groups of long cilia which beat much more strongly than the 

 others. They coincide closely in position with those long cilia 

 which have already been described in the adult (p. 77) which are 

 situated on either side of the gastric shield and keep the ali- 

 mentary matter in circular motion. As was pointed out by 

 Meisenheimer ('01, p. 94), the food material in the stomach of 

 the larva is in constant rotation under the action of the cilia. 

 In Venus and Ostrea this motion is due largely to the action of 

 the two groups of large cilia; it is always in a clockwise direction 

 when viewing the animal from the anterior end. These cilia, 

 both in position and in the direction of their effective stroke, 

 correspond closely, therefore, to those found in the adult. 



When these veligers are placed in water containing carmine 

 grains in suspension, they feed upon it greedily and soon fill the 

 entire alimentary canal. As the color grains enter the stomach 

 they are caught by the large cilia and whipped into the mass 

 of particles and mucus which is whirling in the cavity of this 

 organ. This circular motion is not continuous, for the larvae 

 exhibit spasmodic contractions of the velum and foot, as a re- 

 sult of which the stomach is compressed and the whirling motion 

 ceases for a moment, to be resumed upon the relaxation of the 

 surrounding organs. During the rotation of the alimentary mass 

 the particles of carmine or food matter move slowly posteriorly 

 into the opening of the intestine, where they are caught and car- 

 ried downwards. At this stage there is no indication of the 

 beginning of a separate intestine and style sac. \ 



