I BODY-CAVITIES—NERVOUS SYSTEM 9 
The hinder part of the proboscis-cavity is divided by the 
forward growth of the notochord (Fig. 5, ») into dorsal and ventral 
portions. 
further subdivided into right and left 
halves, the latter typically opening dors- 
ally to the exterior on the proboscis- 
stalk by an asymmetrical “ proboscis-pore ” 
(p.p.). Two symmetrical proboscis-pores 
may, however, occur, or a median pore 
connected with the left division of the 
proboscis-cavity. These may be indi- 
vidual variations within the limits of a 
single species, or may occur as a normal 
feature of a species. 
The collar-cavities open by two “ collar- 
poress /CBig» 13, \¢.p:), situated at: the 
posterior end of the collar, into the first 
pair of gill-pouches, near their external 
opening. Willey has recently described ! 
vestigial pores in relation with the “ peri- 
haemal spaces,” a pair of dorsally situated 
outgrowths of the third body-cavities 
into the collar-region. Narrow “ peri- 
pharyngeal spaces,” also a forward growth 
of the third body-cavities, closely invest 
the pharynx in some species. 
Body-Wall and Nervous System.— 
The body-wall (Fig. 4) consists externally 
of a thick ciliated epidermis (e), con- 
taining numerous gland-cells which secrete 
an abundant mucus. Beneath the epi- 
dermis is a basement-membrane, while 
more internally are layers of muscles, 
whose arrangement differs in different 
parts of the body and in different species. 
The dorsal cavity in extending backwards hecomes 
Fic. 3.—Dorsal view of the 
anterior end of the body of 
Dolichoglossus kowalevskii, 
Kise ee Collate 7s.cir= 
cular nerve ; ¢.p, collar- 
pore ; d, dorsal nerve; g, 
gill-pore ; , notochord ; 
n.s, central nervous sys- 
tem, showing the anterior 
and posterior neuropores ; 
p, proboscis ; p.p, probos- 
cis-pore ; p.s, proboscis- 
stalk ; ¢, trunk ; v, ventral 
nerve. The nerve-plexus 
of the proboscis is repre- 
sented as a black line. 
(After Bateson. ) 
The nervous system consists of a plexus of cells and fibres 
which lie in the basal part of the epidermis of all parts of the 
animal, outside the basement-membrane ; the thicker portions of 
the plexus forming definite nerve-tracts. 
This intimate connexion 
1 Zool. Res. iii. 1899, pp. 273, 280. 
