638 R. C. PUNNETT. 
The nuchal skeleton is strongly developed, occupying a large portion of a transverse 
section in the region of the proboscis stalk (Pl. XLI. fig. 9). The keel is strongly developed 
but much blunted, its side to side diameter being greater than the dorso-ventral one. 
The pericardium is provided with two small “auricles” reaching forward about ~; mm. 
from the main structure on either side. 
Collar. The epithelium of this region is high and fairly well provided with gland-cells. 
The posterior part of the collar on either side of the circular furrow is characterized by a 
more highly glandular zone. In the preserved specimens this region is somewhat paler in 
colour than the rest of the collar. The nerve fibre layer is distinct, whilst, as in the 
proboscis, the basement-membrane is thin. There is no layer of circular muscles outside the 
longitudinal musculature. 
The collar coelom is entirely filled by longitudinal muscle fibres and connective tissue, 
with the exception of a small space round the opening of each of the collar funnels. The 
dorsal septum is complete throughout the entire length of the collar. The ventral septum 
is lacking only at the extreme anterior end (Pl. XLI. fig. 10). 
The median nuchal skeleton is long whilst its cornua are exceedingly short (Pl. XLI. fig. 10), 
a feature in which this genus differs markedly from the remaining members of the family. 
The cornua embrace nearly ? of the total circumference of the cesophagus. 
The collar cord exhibits a well-marked anterior and a smaller posterior neuropore. The 
anterior neuropore especially reaches some way down into the collar (Pl. XLI. fig. 10). 
Towards its hinder limit it becomes somewhat separated off from the nerve cord on the 
dorsal surface of the latter. It is lmed with a definite epithelium somewhat glandular and 
richly provided with cilia. The nerve cord itself is quite solid and is almost entirely sur- 
rounded by a layer of nerve fibres (Pl. XXXVIII. fig. 23). In its hinder portion it shews a 
well-marked ridge projecting up towards the dorsal septum. This ridge is filled with cells 
containing a yellowish-brown pigment. These cells reach a little way into the nerve cord 
and similar cells are also to be found in the perihaemal spaces (PI. XXXVIII. fig. 23). 
Pigment has previously been described by Spengel (98, p. 134 and Taf. 7, figs. 2, 12, 14) 
in the collar cord of Balanoglossus apertus. Without going so far as Willey (99, p. 316) 
in claiming that the dorsal roots are homologues of the vertebrate pineal eyes it is yet 
conceivable that these aggregations of pigment may serve for the perception of light rays. 
Besides this small dorsal ridge there occurs no representative of dorsal roots in W. bisulcata. 
From the anterior part of the collar cord passes off on either side a well-marked nerve 
to the layer of nerve fibrils beneath the cesophageal epithelium. These I have termed the 
cesophageal nerves (Pl. XLII. fig. 16, on.). 
With regard to the histology of the collar cord it may be stated that giant cells, such 
as Spengel (98, p. 609) has described for several species of Enteropneusts, are absent. 
Certain of the ganglion cells near the dorsal surface attain a somewhat larger size, but 
this does not exceed 20—25 yw. Faint vestiges of the remains of cavities in the cord are 
visible here and there under a high power. The pigment referred to above is found along 
the whole length of the cord. 
The perihaemal spaces are well developed and ventrally contain transverse muscle fibres. 
They do not come into contact with one another until just in front of the point where 
the cornua of the nuchal skeleton diverge. Anterior to this they are widely separated by 
the stomochord. 
