APPENDICULARIA FLABELLUM. 



511 



a haemal flexure. In the middle of its haemal aspect the en- 

 doderm of the pharyngeal cavity is raised into a fold, which 

 projects into the blood-cavity contained between the endo- 



Fig. I41.—Appe?idicularia flabellvm. 



I. The entire animal, with the caudal appendage in its ordinary position, or turned 

 forward. 



II. Side view of the hody, with the caudal appendage forcibly bent backward. 



Ai the body; B, the caudal appendage; a, oral aperture; b, the pharynx; c, an 

 atrial opening; d, the corresponding stigma, with its cilia ; e, anus; /, rectum ; 

 g } oesophagus ; A, i, stomach ; k, testis ; I, urochord ; m, cellular patch at the 

 side of the oral end of the body; n, endostyle; p, ganglion ; q, ciliated sac; r, 

 otocyst ; s, posterior nerve with its ganglia, t ; en, endoderm ; ec, ectoderm. 



derm and ectoderm. The walls of the bottom of the fold are 

 thicker than the rest, so that, viewed sideways, it has the 

 aspect of a hollow cylinder. This is the endostyle. 1 (Fig. 

 147, n.) 



1 So described and named in my " Observations upon the Anatomy and 

 Physiology of Salpa and Pyrosoma, together with Remarks upon Doliolum 

 and Appendicularia." ("Phil. Trans.," 1851.) In 1856, however, I stated; 

 "With regard to the endostyle, I have nothing important to add tomy pre- 

 vious account, except that I believe it to be here, as in other Ascidians, the 

 optical expression of the thickened bottom of a fold or groove of the branchial 

 sac." ( Quarterly Journal of Microscopical Science, April, 1856.) In my memoir 

 on Pyrosoma ("Linn. Trans.," 1860, p. 205), the endostyle is stated to be " in 



