330 
ZOOLOGY OF THE FAR EAST. 
so important a function as that of respiration could be assigned to a structure, which 
on the sHghtest provocation is thrown oflF completely in Echiurus pallasii, and is 
absent in some of the species of the genus Thalassema, as T. vergrande, and in the 
aberrent genus Saccosoma. 
From the structure of the proboscis of the three species described above, 
it would be seen that the large development of the sinuses is correlated with the 
development and evolution of the gills. A few sinuses of this type are figured by 
Embletonfor E. tmicinctus and the two lateral ones are of common occurrence in the 
various species of Thalassema and other genera of Echiuroids. It has also been 
shown that these sinuses are in open communication with the general body cavity 
and are continuous with the cavities of the gills ; and further that they have no 
connection with the closed blood- vascular system. The presence of coelomic cor- 
puscles in their cavity and the red colour in the living animals shows that the coelomic 
fluid is constantly passing through them. The coelomic fluid would undoubtedly be 
of great use in making the proboscis firmer, but the chief use of the sinus connections 
and the development of hollow gill-like outgrowths seems to be the aeration of the 
coelomic fluid, a function which was assumed by the authors noted above though in 
a different way. The ciliated cells would also be of use in wafting the food particles 
to the mouth. It may also be remarked here that no indication that the proboscis 
can be thrown off was observed in the living sp2cimsfis of the three species here 
discussed. 
The possession of gills by these forms was considered by Annandale and Kemp 
as being possibly a character of sufficient validity to separate them into a new genus, 
though this course was not adopted by them. In view of what has been stated 
above and the closs general resemblance of the anatomy of this group to that of the 
other species of the genus Thalassemi I am not disposed to separate them into a new 
genus, but these brackish water species form a distinct group, of which T. dendrorhyn- 
chus may be taken as the type. 
Stephenson (14) in confirmation of Michaelsen's view considers the gill-like pro- 
cesses of the freshwater Oligochaeta of little value as characters of generic importance, 
owing to the great variation exhibited by these structures both as regards situation 
and even in different specimens of the same species. The learned author in the course 
of a conversation further remarked that this view may possibly have a more general 
application in the case of other groups of animals living under similar circumstances, 
a view with which I am in entire agreement. 
In considering the meaning of the peculiarities of the proboscis in this group it is 
important to bear in mind that the three species live in peculiar but similar types of 
environment. T. sabinum has been found only in the Tale Sap on the east coast of 
Peninsular Siam. The Tale Sap is a shallow lagoon the water of which varies in 
salinity with tide and season and is always muddy. In the outer and intermediate 
parts of the lake to which the Echiuroid is probably confined, the specific gravity ' 
1 All the specific gravities here cited have been corrected to a standard temperature of I5°C. See Annandale and 
Kemp, Mem. Jiid. Mus. V, p. 17. (iqi;). 
