52 



Fig. 14. Concretions from renal vesicles. X 200. 

 Fig. 15. Bunch of spermatic tubules from testis. X 50. 



Plate V. 

 Reference letters. — ar. arcbenteron, at. atrial in- 

 volution, . ail. otolitb, be. blastocoele, bp. blastopore, 

 ch. notochord, ep. epiblast, /. tail fin, foil, follicle cell, 

 hy. hypoblast, i. intestine, ??i. mouth, 7nes. mesoblast, 

 muse, muscle cells, mb. mesoblast layer, mc. mesoblast 

 cell, n. nucleus of ovum, nc. neural canal, n.ex. neuren- 

 teric canal, 7i. ch. notochord, ?i.v. cerebral vesicle, oc. 

 cerebral eye, p. protoplasm of ovum, s. spermatozoon, t.c. 

 " testa " cells of ovum. 



Fig. 1. Mature ovum and spermatozoon of Ascidia, 

 Fig. 2. A segmentation stage, in section, to show blas- 



tula. 

 Fig. 3. Early gastrula stage. 

 Fig. 4. Later gastrula stage. 



In these and some of the other figures, the 

 clear cells indicate the notochord, the hypo- 

 blast cells have small circles, and the nerve 

 cells are marked with obhque lines, while the 

 mesoblast cells are cross hatched. 

 Fig. 5. A later embryo, showing rudiments of noto- 

 chord and nervous system. 

 Embryo showing body and tail, &c. 

 Transverse section of the tail of larva. 

 7a. Transverse section of the body of embryo. 

 Embryo ready to be hatched. 

 Free-swinnning tailed larva. 

 The metamorphosis — larva attached to a stone. 

 Tail and nervous system of larva degenerating. 

 Further degeneration and metamorphosis of 

 larva into 

 Fig. 13. tlie young fixed Ascidian. 



