ON TUB STRUCTURE OF CERATELLA FUSCA (GRAY). 23 



Fig. 5. Portion of the skeleton of a somewhat larger branch showing the 

 chitinous network of which it is composed and the little bracket-like hydrophores. 

 (Hy.) x 12. 



Fig. 6. Highly magnified small portion of a branch seen partly by direct and 

 partly by transmitted light. Two gastrozooids are shown each of which is placed upon 

 a hydrophore. The latter shows prominent ribs which project beyond the margin 

 and arc connected by a thin fenestrated web of chitin. Two male gonophores arise 

 from the cccnosarc and they and the gastrozooids are quite naked. The whole branch 

 is covered by a thin external layer of ectoderm, x 20. 



G. gastrozooids. Gon. gonophore. E. external layer of ectoderm. Hy. hydro- 

 phore. Hy. 1 web connecting the ribs of the latter. 



Fig. 7. Transverse section across the body of a gastrozooid. The tentacles 

 are solid with swollen ectoderm ends filled with thread cells. The zooid has been 

 feeding and the endoderm cells are full of little food particles. F. Remnant of 

 small crustacean on which the zooid is feeding. It lies close against the endoderm 

 on one side and the food particles are passing into the interior of the cells. Outline 

 drawn with Camera, Zeiss E, oc. 2. 



Fig. 8. Transverse section across a gouophore. Mn. endoderm of the 

 manubrium. Sp. sperm cells in the ectoderm of the latter. Ect. ectoderm of the 

 medusa. R. radial canals. Ect. ectoderm of the sub-umbrella surface. Outline 

 drawn with Camera, Zeiss E, oc. 2. 



PLATE IIIA. 



Fig. 9. Semi-diagrammatic drawing of a longitudinal section through a 

 small branch. The skeleton is coloured brown the soft parts grey. E. external 

 layer of ectoderm. Gon. gonophore. G. gastrozooid. Hy. hydrophore. Sk. 

 general network of skeleton cut across in various directions. Outline drawn with 

 Camera, Zeiss A*, oc. 2. 



Fig. 10. Semi-diagrammatic drawing of a transverse section across a good-sized 

 branch. Letters as in figure 9. Ect. ectoderm of endosarc tubes. End. endoderm. 

 Outline drawn with Camera, Zeiss A*, oc. 2. 



Fig. 11. More highly magnified portion of a branch cut in transverse section. 

 The ectoderm of the gastrozooid is directly continuous with the external layer of the 

 branch and the base of the zooid is continuous with two of the coenosarc tubes. 

 At C. is represented the characteristic feature of the latter crossing over live 

 connecting strands of the chitinous network. C. points at which the soft parts 



