356 



C. FORSTER COOPER. 



On each bridge of tissue between the gill slits the branchial epithelium projects as a mass 

 of large columnar cells with darkly staining nuclei (Fig. 88). Many sections, but by no means 

 all, give an appearance of having the branchial epithelium split into two (Fig. 89)^ The latter 

 extends alternately down each side of a slit, so that every slit has the branchial epithelium 



PH. 



C.S.G 



End. 



--M 



BR.E - 



G.S.I 



Fig. 86. 



Fio. 87. 



MET. 



Fio. 88. 



Fig. 86. Larva. Section through the extreme posterior end of the preoral pit (PP.), showing Hatschek's nephridium 

 (N), the commencing formation of the endostyle {End.) and the two prolongations of the pharynx (PH.). 



FiQ. 87. Larva. Transverse section passing through the mouth (Jl/) and first gill slit (G.S.I.). The two arms of 

 the club-shaped gland {C.S.G.) are also shown. 



Fio. 88. Larva. Section through a part between two gill slits showing the metapleural folds {MET.) and the 

 branchial epithelium {B.R.E.). 



on the opposite side to the one preceding and following it. The meaning of this is not clear, 

 and can only be solved satisfactorily by the examination of later stages. 



Springing from the middle of the pharynx are the true hyper-pharyngeal bands. The 

 left-hand band arises immediately behind the 

 mouth, that on the right hand commencing 

 directly behind the club-shaped gland. They 

 both extend through the whole length of the 

 pharynx, and die out at the beginning of the 

 intestine. The latter itself is normal. The 

 glandular patch in the rectum in all these 

 larvae is very noticeable. 



In a later stage (PI. XVIII. figs. 4 and 

 5), also having GO myotomes, various changes 

 are found to have taken place. The endostyle 

 has become fully formed, and has acquired 

 all the essential histological features found in the adult. It still, however, lies in the larval 

 1 I am unable to say whether this phenomenon has any real meaning, or is merely due to the combined effects of 

 preservation and section cutting. 



BR.E. 



BR.E 



Fig. 89. Larva. Section to the right through a gill slit and 

 to the left intermediate to two slits. The left section 

 shows the appearance of splitting found occasionally in 

 the branchial epithelium. 



