SEA-FISHERIES LABORATORY. 205 
As the stomach contracts to form this division of the 
intestine, two folds of its wall (fig. 11, Pl. III.), which 
are anterior and posterior, are formed, and are continued 
down the straight intestine dividing the lumen of the 
latter into two longitudinal cavities, both of which com- 
municate with the stomach by wide openings and with 
each other by a long wide slit. Of the two communicating ~ 
semi-tubes so formed, the left (Al.c.3’) is the larger, and 
is exactly circular in transverse section; it lodges the 
crystalline style. The right semi-tube (Al.c.3”) is irre- 
gular in section, and forms the channel along which the 
ingested food travels. Morphologically, this is the portion 
of the intestine immediately following the stomach. The 
left semi-tube is a diverticulum of the stomach cavity— 
the pyloric caecum* (sac of the crystalline style). Pyloric 
caecum and intestine are separate in some Lamellibranchs 
(Pholas, Donaz), but in Cardiwm and others have fused 
together, the anterior and posterior folds being the remains 
of the primitively adjacent walls. At the tip of the straight 
intestine, in the short caecum already referred to, is a 
vestige of the originally separate condition of the two 
channels. 
Three very distinct kinds of epithelium are present in 
the straight portion of the intestine. On the wall of the sac 
of the crystalline style there is a single layer of spindle- 
shaped cells (Hp.J.1, fig. 12, Pl. III.), having an average 
height of about 0'(03 mm. These bear a very close set 
series of long and stiff cilia, having an average length of 
% that of the cells carrying them. The cell bodies are 
finely granular, with rather highly refractive free borders, 
the nuclei are situated at their lower extremities ; the cells 
fit together very closely, except at their lower extremities, 
* Purdie, A. Studies in Biology for New Zealand Students. No, 3. 
Anatomy of the common Mussels. Wellington, 1887. 
