51 



Fig. 4 is a Botryliid colony {Botryllus) . 



Fig. 5 shows the union of two Ascidiozooids, in a Com- 

 pound Ascidian colony, to form a common 

 cloaca (c.c.) in the common test. 



Figs. 6 to 8 show the three forms of body found amongst 

 the Ascidiozooids of Compound Ascidians. 



Fig. 6 is from a Botryliid colony. 



Fig. 7 is from a Distomid colony. 



Fig. 8 is from a Polyclinid colony (all from right side, 

 magnified). 



Fig. 9. Section through outer part of test of Asoidia to 

 show " vessels " and " bladder " cells. X 50. 



Fig, 10. Diagram of Ascidia to show the arrangement 

 of the blood system, from left side, in correct 

 morphological position for comparison with 

 Vertebrates. 



Plate IV. 



Fig. 1. Part of branchial sac of Ascidia vienttda, from 



the outside. X 50. 

 Fig. 2. Part of branchial sac of Ascidia mentiila from 



the inside. X 50. 

 Small part of last. X 300. 

 Part of the dorsal lamina. X 40. 

 Transverse section of the endostyle, X 200. 

 Blood corpuscles oi Ascidia. 

 Part of section of wall of intestine showing 



refringent organ, spermatic tubules, &c. 

 Ocellus from the branchial aperture, in section. 

 The heart and pericardium, in side view. 

 The heart and pericardium, in section. 

 Group of renal vesicles, X 50. 

 Part of a renal vesicle, more highly magnified. 

 Two cells from wall of renal vesicle, 



