52 HAROLD SELLERS COLTON. 



DESCRIPTION OF PLATES. 



The figures were all drawn with a Zeiss microscope and apocromatic lenses. In 

 making all the drawings a camera lucida and artificial light was used, in the case 

 of Botryllus a Welsbach burner, and in the case of the other forms an ordinary oil 

 lamp. With the exception of Fig. i, Fig. 16 and Fig. 17 all were drawn at a mag- 

 nification of 1,500 diameters, and have been reduced in reproduction to 1,000. 

 .4 = ampullae. PS == peribranchial sac. 



= blood cell. R rectum. 



C = concretions of indigo carmin. RT = rectal tubules. 



= intestine. RO = pyloric gland. 



Nu = nucleus. S = stomach. 



= (Esophagus. V = vacuole in intestinal cell. 



PC = pyloric ccecum. 



EXPLANATION OF PLATE I. 



FIG. i. The stomach and intestine of Bolryllus. X 52. 



FIG. 2. Two ampulla? of the pyloric gland in Botryllus. This drawing shows 

 the long whip-like flagella and also the granules in the cells. X 1,000. 



FIG. 3. Portion of one of the main ducts. X 1,000. 



FIGS. 4-7. Optical section of a rectal tubule showing segmentation, granules, 

 and flagella. X 1,000. 



FIG. 8. Optical section of a termination of a rectal tubule showing a thin place 

 in the wall of the tube. X 1,000. 



FIG. 9. Optical section of a cup- like depression in the end of a tubule. < 1,000. 



FIG. 10. Optical section of a tube with two cup-like depressions at the end. 

 X 1,000 



FIGS. ii-i2. Termination with a single cup-like depression. X 1,000. 



FIG. 13. Optical section of a segmented tube in the walls of which there are 

 no granules. X 1,000. 



