50 



r. rectum. tn. tentacle. 



ren. renal vesicles. t.k. terminal knobs on vessels. 



sg. stigmata. tr. transverse vessels. 



sp. testis. t.v. test vessel. 



sph. sphincter. ty. typhlosole. 



St. stomach. v. vessel. 



t. test. v.app. vascular appendage. 



t.c. test cells. v.bl.s. ventral blood sinus. 



Fig. 1. Diagram of the outside oiAscidia, from right side. 



Fig. 2. Transverse section through the atrial aperture 

 to show arrangement of internal cavities and 

 organs. (To avoid complication the internal 

 longitudinal bars are not represented in the 

 branchial sac.) 



Fig. 3. A mesh of the branchial sac, diagrammatic. 



A. From the inner surface. B. In section. 



Fig. 4. Diagrammatic dissection to show the structure 

 oi Ascidia (compare with fig. 2). 



Fig. 5. Section through test and mantle (body-wall) to 

 show the relations of the ectoderm and meso- 

 derm to the test. 



Fig. 6. Sagittal section through antero-doi'sal part of 

 body to show relations of nerve ganglion, 

 neural gland, &c. 



Fig. 7. Dorsal front of pharynx from inside, to show 

 dorsal tubercle, tentacles, and neighbouring 

 parts. X 50. 



Plate III. 



Figs. 1 to 4 show typical examples of four important 



families of Compound Ascidians, natural size. 

 Fig. 1 is a Distomid colony {Colella). 

 Fig. 2 is a Didemnid colony {LeptocUmun). 

 Fig. 3 is a Polyclinid colony {Pharyngodictyon) . 



