74 CASWELL GRAVE 



cells, and in cells of other parts of the body also, varies greatly 

 in tadpoles of different broods, those liberated by highly colored 

 colonies being more highly pigmented than those produced by 

 colonies of lighter color. The pigmentation of each tadpole is 

 approximately the same as that of its parent colony. 



The part of the tunic which envelops the tail is greatly com- 

 pressed dorsoventrally and expanded in the horizontal plane 

 and entirely constitutes the comparatively wide tail fin of the 

 tadpole. Seeliger ('85), in his study of Clavellina, noted that 

 the tunic substance is secreted during the embryonic period when 

 the tail is folded forward and closely compressed between the 

 body of the embryo and its chorionic membrane and that the 

 part which is secreted about the tail is thus caused mechanically 

 to he spread out on either side and to take on a compressed fin- 

 like form. He also noted that the entire tail, the fin included, is 

 twisted on its axis to the left during the embryonic period, but, in 

 the Clavellina tadpole, it apparently untwists when the chorion 

 is ruptured at the time of hatching, for he describes the tail fin of 

 the free-swimming larva as having a vertical position. Damas 

 ('04) noted the horizontal position of the tail fin of the larva 

 of Distapha magnilarva and called attention to its similarity in 

 this respect to Appendicularia. 



The part of the tunic surrounding the body of the tadpole is 

 laterally compressed, but the right and left sides are slightly 

 asymmetrical. Viewed from the dorsal side, a shallow concave 

 depression is seen on the left near the anterior end, and the 

 anterior tip end of the tunic which contains the middle adhesive 

 papilla is found to lie slightly to the right of the medial sagittal 

 plane of the body (fig. A). These asjniimetrical features are 

 the result of the pressure of the tail during the period of embry- 

 onic development when it is bent forward beneath the chori- 

 onic membrane and coiled about the anterior part of the tunic 

 (fig. B). The imprint of the tail in the tunic takes an oblique 

 course from below upward across the left side, and therefore 

 gives to the tunic the form of a screw with a single groove. 



