426 ZOOLOGY 
species which is in the main described below is B. kowalevski, 
which, together with B. brooksii, is found on the east coast of 
the United States. 
Balanoglossus differs from other members of the phylum 
with which it is grouped in the fact that its body is covered 
externally with cilia, and in this respect it resembles a Nemer- 
tine. The ciliated epidermis contains a considerable number 
of unicellular mucous glands, which secrete a very copious 
mucus. This secretion serves to line the tubes in the sand 
and mud in which the animal lives. In one species the 
mucus hardens into a definite tube, in the walls of which 
grains of sand are embedded. The body of Balanoglossus has 
usually a very characteristic odour. 
The body-cavity or coelom consists of a single unpaired 
portion occupying the proboscis, a paired portion in the collar, 
and a paired portion in the trunk. These are derived from 
five coelomic pouches of the archenteron of the embryo. The 
original cavities of these are, however, much obliterated by the 
growth of stellate connective tissue cells (Fig. 245). The spaces 
: Fia. 245.—Section, partly diagrammatic, through 
$+ 7-3 the respiratory part of the trunk of Balano- 
Zz NS glossus. The whole course of a gill-slit 
a 8 could not be seen in a transverse section, as 
the slits run obliquely. 
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1. Dorsal portion of alimentary canal. 7. Nerve plexus at the base of the skin. 
2. Ventral portion of alimentary canal. 8. Longitudinal muscle fibres. 
3. Dorsal nerve cord, in the skin. 9. Connective tissue cells filling up the 
4, Dorsal blood-vessel. coelom. 
5. Ovary. 10. Ventral blood-vessel. 
6. Gill-slit. 11. Ventral nerve in the skin. 
between the cells communicate with the exterior in the pro- 
boscis by a ciliated proboscis pore,—in one species this is 
paired,—and the right and left collar cavities open to the 
exterior by a right and left ciliated collar pore. These latter 
