300 JAMES RANKIN, On the supposed Vertebration of he Tuil in Appendicularia. 



Explanation of Plate. 



Reference letters): 



eg Caudal ganglion. m. I Muscle layer. 



C.ch Cells of notochord. w Nuclei. 



ch Notochord. n.f Nerve filament. 



C. n. f Corpuscles on nerve filament. nu. c Nucleated cells in alary ex- 



ep Epithelium. pansion of tail. 



f.m.l Fibrous part of muscle layer, nu.ch Nuclei of notochord. 



gl. C Gland cells. Ppl Protoplasmic part of muscle 



i. m. I Interruptions in muscle layer. layer. 



is „Islands". r Reticulations (nuclei of mus- 



m.'fi Muscle cells. cle cells). 



Plate /f. '^ 



Fig. 1. Tail of Fritillaria furcata. The muscle layers of this 

 specimen showed no interruptions. Oc, 2, Obj. 3. 



Fig. 2. Tail of Oikopleura dioica showing eight interruptions in 

 the musculature. Oc. 4, Obj. 3. 



Fig. 3. Notochord, nerve filament, caudal ganglion, and nerve cor- 

 puscles of tail of 0. dioica. Showing unequal distribution of nerve 

 corpuscles. From living specimen. 



Fig. 4. Part of muscle layer of tail of 0. dioica. The inter- 

 ruption extends only half way across the layer. Oc. 4, Obj. 7a. Re- 

 duced one half. 



Fig. 5. Part of muscle layer from tail of 0. dioica. Three 

 "islands" are shown. Oc. 4, Obj. 3. 



Fig. 6. Part of tail of 0. dioica showing reticular arrangement 

 of nuclei of muscle cells. Oc. 4, Obj. 7a. 



Fig. 7. Part of tail of 0. dioica. Posterior extremity of noto- 

 chord showing nucleated cells. Oc. 4, PL 7a. 



Fig. 8. Posterior part of nerve filament from tail of F. furcata 

 showing character of nerve corpuscles in this species. Oc. 4, Obj. 7a. 



Fig. 9. Part of transverse section of tail of 0. dioica to show 

 structure of muscle layer. Oc. 4, Obj. 18b. 



Fig. 10. Part of tail of very young 0. dioica. Oc. 4, Obj. 7a. 



The drawings, except Fig. 3, were all made by means of Reicueet's 

 camera lucida and lenses. 



*rouini»no«obo Burhdruckorel (.U»nii»nii PohU)lnJou». — IS21. 



