PHYLUM CHORDATA 



139 



B 



specimens of Myxine thrown into a bucket of water are capable 

 of gelatinising the whole with their secretion. The slime-glands 

 of Myxine contain peculiar "thread-cells" containing a much- 

 coiled thread which unwinds either before or after the discharge 

 of the cell from the gland. 



Myxine approaches most nearly to the condition of an internal 

 parasite of any Vertebrate ; it is said to attach itself to living 

 Fishes and gradually to 

 bore its way into the 

 coelome, devouring the 

 flesh as it goes. 



There is no true buccal 

 funnel : the space on 

 which the mouth opens 

 is edged with tentacles 

 (Fig. 806) supported by 

 cartilages ; there is a 

 single median tooth 

 above the oral aperture, 

 and two rows of smaller 

 teeth on the tongue. The 

 papillas beneath the cone- 

 like horny teeth bear a 

 still closer superficial re- 

 semblance to rudiments 

 (or vestiges) of true cal- 

 cified teeth than is the 

 case in the Lamprey ; but 

 it appears that no odon- 

 toblasts and no calcified 

 substance of any kind 

 are formed in connection 

 with them. The nostril 

 (na. ap.) is a large un- 

 paired aperture situated 

 in the dorsal margin of 

 the buccal space, and 

 is continued into a pas- 

 sage, the pituitary sac, 



which opens into the pharynx. Myxine commonly lives nearly 

 buried in mud, and the respiratory current passes through this 

 passage to the gills. 



The only fin is a narrow caudal surrounding the end of the tail. 

 The respiratory organs present striking differences in the two 

 genera. In Bdellostoma there are in different species six to 

 fourteen very small external branchial apertures (Ir. cl. 1) on each 

 side, each of which communicates by a short tube with one of 



br.cl.f — ' 



br.a-p 



t.ct.d. 



Fig. 806.— Head of Myxine glutinosa (A) and of 

 Bdellostoma forsteri (B), from beneath, hr. aji. 

 branchial aperture ; hr. cl. 1, first branchial cleft ; 

 •)nth. mouth ; na. ap. nasal aperture ; as. ct. d. oaao- 

 phageo-cutaneous duct. The smaller openings in A 

 are those of the mucus-glands. (After W. K. 'Parker.) 



