of which none was seven-capsuled, only two were five-capsuled, 

 and more than three-quarters were single-capsuled. 



When first laid the egg is less than 0.1 mm. in diameter. Divi- 

 sion may be clearly seen through the transparent case, and within 

 twenty-four hours the egg becomes multicellular. During the 

 fourth day the embryo begins to rotate slowly. Although the 

 cilia were not seen, the result of their motion w^as plain when small 

 particles in the fluid in which the embryos float, came in contact 

 with, and were cast away from, those portions of the embryo 

 which bore cilia, particularly that portion eventually becoming 

 the mouth. When ciliary motion begins the embryo is still approx- 

 imately spherical. With the single exception of one egg-case with 

 one capsule containing five eggs, no capsules were seen with more 

 than one egg. In this abnormal case (Plate 2, fig. 7) one of the 

 five eggs broke into several small fragments within twenty-four 

 hours after being laid. The four others continued to increase in 

 size and in four days all were revolving slowly. All were then of 

 approximately the same size and were also as large as embryos 

 of the same age in normal capsules. Only one of the four, however, 

 showed normal division ; the others, although rotating in a manner 

 identical with the normal embryo, were very transparent. Abnor- 

 mal development had not prevented cilia from developing and 

 functioning. The abnormal eggs one by one, broke down within 

 48 hours after ciliary motion had begun and the fragments were 

 scattered through the fluid of the capsule. The one remaining 

 apparently normal embryo continued to develop, finally reaching 

 the stage where muscular motion begins. After 24 hours of com- 

 bined ciliary and muscular motion the embryo came to rest in one 

 corner of the capsule. The cilia continued to beat for six hours 

 and then stopped; when the embryo quickly disintegrated. 



When ciliary motion begins on the fourth day, the embryo is 

 about 0.2 mm. in diameter. This motion continues steadily, 

 while the embryo increases in size, but continues spherical, until 

 the sixth day when it becomes gradually more elongate. On the 

 seventh day it is very easy to distinguish two well-marked divi- 

 sions of the foot (Plate 2, fig. 4). During the eighth day muscular 

 motion begins and a twisting and turning of the animal takes 

 place, together with a gradual diminishing of the rotation (Plate 

 2, fig. 5). The embryo is now 0.5 mm. in length. In a few hours 

 rapid changes occur, protuberances which later become the ten- 

 tacles are formed, and the viscera are more easily distinguished 

 from the muscular portion of the foot. Soon the foot can be seen 



