LYMPHATIC GLAND. 
339 
The concretions are translucent in Cydostoma costulatum, but 
only occasionally so in Cydostoma elegans, they may, however, be 
rendered transparent and their complex structure demonstrated by 
immersion in weak alkaline solutions. Ammonia, Potass or Soda 
water. They dissolve instantly without effervescence in Sulphuric 
acid, and the various reactions show the concretions to be almost 
entirely composed of Uric acid. 
The interspaces between the concretions are filled with a grey mass 
of immobile Bacilli, three to four g long, which however exhibit 
Brownian movements. They are variable 
in size and shape and often united 
together in pairs, and their constant 
presence in this closed cavity contain- 
ing so much alternately deposited and 
re-absorbed Uric acid, would seem to 
indicate symbiotic action, the bacilli having probably some impor- 
tant function either in connection with the deposition or the 
re-absorption of the Uric acid concretions. 
The Lymphatic Gland {lympha, water) or spleen, the formative 
organ of the ammbocytes or white blood corpuscles, thougli present 
in our land and fluviatile species, is not so distinctly localized as in 
the Opisthobranchs, the lymphatic cells being more generally difi’used 
throughout the connective tissue, though usually most numerous and 
active in or near the respiratory organs, especially along the course of 
the afferent cardiac vessels and upon or near the auricle, and hence 
it has been termed the “ Gland of Auricle” by some observers. 
Although the grouping of the lymphatic cells is so variable in 
character, their aggregations are always constituted by a layer or 
stratum of connective tissue, crowded with nuclei, which become 
invested by protoplasm containing refractive ferment granules, the 
amoebocytes eventually passing through the meshes or interstices of 
the connective tissue and falling into the blood stream. 
In Dreissensia this sanguineous or blood-making gland, as it has 
been termed, is in the gill itself, close to the afferent vessels, but in 
the Gastropoda it varies greatly in position. In Limax and Helix the 
gland occurs as a thick stroma surrounding all the efferent pulmonary 
vessels ; but in the Lhnncddw the gland is not distinctly separable 
from the pulmonary vessels. In our Streptoneures the lymphatic organ 
may have a dual develojiment, being not only represented along the 
> 
Fig. 632. — Bacilli of Gland of 
Concretion of Cydostoma elegans 
(Mull.), highly magnified (after 
Garnault). 
