328 
ZOOLOGY OF THE FAR EAST. 
space is occupied by the massive connective tissue (C.t) in which we can distinguish 
structurally an outer and an inner portion. The outer one, which is much the smaller 
and thinner of the two, consists largely of connective tissue-cells of an irregularly 
polygonal shape ; some, however, are distinctly multipolar. The cells are either fused 
with one another or connected by short processes. The more deeply situated cells, 
which may be described as a gradation between the outer cells and the internally 
situated connective tissue-fibres, have longer processes. The number of cells in this 
part is fewer and their fibres form a loose connective tissue. Here and there nerve- 
cells and a few pigment corpuscles are also to be seen in this portion of the connec- 
tive tissue. The fibres are sinuous, and in the middle have a dorso- ventral course, 
while outside they run more in a longitudinal direction. The connective tissue portion 
in T. branchiorhynchus has a large number of lacunar spaces in the basal gill-bearing 
portion of the proboscis, further forwards the tissue is much more compact and very 
few lacunae are visible. The number of these spaces is far fewer in the proboscis of 
T. dendrorhynchus, while practically none could be seen in T. neptuni. 
Below this deeply situated portion of the connective tissue, the various layers 
enumerated above appear in a reversed order till we reach the epithelium {C.e.) of the 
ventral surface, which as has been remarked before consists of ciliated cells. These 
cells are present only on the ventral surface of the proboscis and on the gills. They 
are of the same type as the columnar epithelium of the dorsal surface of the proboscis 
but are more elongated, measuring 14 by 6 and the nucleus is ovoid. 
Before describing the histological structure of the gills it is necessary to describe 
the large number of lacunar spaces {La.) which are present in the proboscis of these 
forms a little above the ventral surface. These spaces, however, are quite distinct 
from the spaces in the connective tissue mentioned above, and from the blood-vessels 
of the proboscis to be described later. At the point of j unction of the proboscis with 
the body they consist of two large spaces in direct continuation of the body cavity. 
Further on the spaces become divided into a large number of small compartments of 
a triangular or quadrangular outline, and separated from one another by thin septa ; 
as we reach the tip of the proboscis, the adjacent spaces have begun to unite until at 
the end only a single space is to be seen. The number of these spaces is much larger 
in T. branchiorhynchus than in T. dendrorhynchus. The spaces are situated near the 
ventral margin above the muscular strata and often contain large number of coelomic 
corpuscles. The outermost of these spaces contain the lateral blood-vessels of the pro- 
boscis, and their cavity is continuous with the cavity of the gills (fig. 6) ; the blood 
vessels which run through these cavities to the anterior end are held in position by a 
distinct connection of connective tissue. 
The gills {Gi) of T. branchiorhynchus are hollow filiform outgrowths from the 
lateral margins of the proboscis an-d in some cases from the ventral surface near the 
edge. The filiform proces.ses by further branching and division give rise to the much 
divided arborescent structures, which are present in this species. The structure of 
these gills is peculiar. Near the origin they have an outer covering of ciliated epi- 
thelial cells of the same nature as those on the ventral surface of the proboscis, and 
