KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 52. N:0 I[6. 37 
Anatomy of Chamostrea plicifera. 
In the inner organisation (fig. 5), Chamostrea exhibited many peculiarities. 
Considering first the intestinal canal, we find the stomach in its dorsal part extended 
transversly; further down it widens in its central part, but keeps a deep furrow on 
each side. The left one soon becomes separated from the stomach proper and 
extends as a coecal appendage (fig. 5c. 1.) towards the front; the right furrow also 
gives rise to a coecum, which is, however, much shorter. The central or pyloric 
part of the stomach gives off a short, median, anterior, descendent, principal liver 
duct (/. c.) and passes on downwards as the duodenal portion, showing a very narrow 
furrow in its anterior side, somewhat to the right of the median line. The chief 
part of the duodenal portion is occupied by the wide furrow of the crystalline stylet. 
In this specimen it contained only a cuticula separated from the underlying cylindric 
epithelium. In the lower end of the duodenum, this sheath of the crystalline stylet 
widens somewhat to a smal] sac; this probably marks the first step of a separation 
into a crystalline coecum. Beneath this sac-like dilatation the intestine emanates, 
describes a short curve towards the front, and passes by a simple flexure below and 
behind the duodenum towards the dorsal side of the pericardium, and then continues 
as rectum to the anus on the hinder side of the posterior adductor. 
The liver (/.) occupies the central part of the visceral hump in front and at 
the sides of the upper part of the duodenum and of the stomach. From its upper 
portion there debouch two separate anterior and one posterior liver duct into the 
right part of the stomach and from its lower portion the somewhat larger principal 
liver duct leads to the left side of the cardiac part of the stomach. 
The oesophagus (oe.) has its walls folded just above the mouth; well towards 
the interior they become smooth. The labial palps (/. p.) are strongly folded. 
The gills and the circulatory organs (fig. 6). As mentioned, there are two 
demi-branchs on each side of the body, the posterior one consisting of only one 
lamella, the anterior of two, as usual. The posterior demi-branch is to be considered 
as originating in such manner that its descendent lamella is probably greatly reduced 
in size in analogy with the conditions prevailing in Pisidium. In their detailed organ- 
ization the gills in many respects recall those of Chama: the anterior demi-branch 
has a marginal furrow in its under free margin, and each lamella is plaited, the 
largest folds containing about 18 filaments, and lastly the principal filaments contain 
alternately afferent and efferent blood vessels. But by a study of the organization 
as a whole, essential differences between the present species and a Chama are to be 
established. It is not sufficient to examine a single section through the gills to gain 
an idea of the detailed organization and the combinations of filaments and lamellae. 
We must also consider in what manner the blood vessels enter into and leave the 
respiratory organs, and not until such an examination has been made can the com- 
plete structure of these organs be revealed and exhaustively compared with that of 
other forms. 
