105 ERNEST WARREN. 



fixed with hot corrosive or Fleimning's sohition ; but it may 

 be observed during- life. Very possibly this character is also 

 possessed by the typical C. roscoffeiisis. 



In the vestibule the ectoderm is only thinly clothed with 

 cilia^ and they nre only about half the height of those on the 

 rest of the ectoderm (fig. 5, c f., c. t\and c. 6.). The general 

 ectoderm is so closely packed with cilia that they constitute 

 a definite layer (c. h.), which, in section appears as thick or 

 thicker than the ectoderm cells themselves. The difi^erence 

 in this respect between the ectoderm of the vestibule and the 

 general ectoderm is very apparent. The average size of 

 mature specimens alive is about 4 mm. in length and 0"85 mm. 

 in breadth. The usual length of the large sagittocysts is 

 about 30u. The animal undoubtedly feeds on diatoms (fig. 2 

 and fig. 3/.) and other unicellular organisms, in addition to 

 any nutritive substances it may obtain from the chlorophyll 

 bodies. 



All stages of growth were collected both in September and 

 in May. When very young the animal resembles a ciliated 

 planula (fig. 1) in general appearance, and I could observe 

 no obvious differentiation of organs or tissues, save into a 

 ciliated ectoderm and a homogeneous inner mass of cells. 

 The first sign of differentiation to appear is a row of four or 

 five cells on each side just behind the oral aperture. These 

 are the germinal cells which will develop into the ova (figs. 2 

 and 5, g. c). The germinal cells, which will form the scattered 

 testes, seem to originate at a later period in their definitive 

 position, and do not appear to arise from the two .rows of cells 

 above mentioned. The ova, during their growth and matura- 

 tion, are remarkable for their branched and stellate condition 

 (fig. 8, d.o.). I suggest that this is associated with the fact 

 that there appear to be no follicle or feeding cells, and con- 

 sequently the ova themselves obtain their nourishment by 

 sending out pseudopodia into the surrounding parenchyma. 



The drawings on the accompanying plate have been made 

 chiefly for the purpose of illustrating the peculiar amoeboid 

 character of the ova. 



