268 ARACHNIDA—-XIPHOSURA CHAP. 
walking legs, and these by an alternate motion “card” the food 
into fragments, which when sufficiently comminuted pass into the 
mouth. At times its appendages are caught between the valves 
of Venus mercenaria, a burrowing bivalve known in America as 
the “ quahog” or “round clam.” The Zamulus has seized with 
its chelate claws the protruding siphon of this mollusc, which, 
being rapidly drawn in, drags with it the limb of the king-crab, 
and the valves of the clam are swiftly snapped to. 
As a rule in Arachnids the alimentary canal is no longer 
than the body, and runs straight from mouth to anus, but in 
Limulus, the mouth being pushed far backward, there is a median 
loop, and the narrow oesophagus which leads from the mouth, 
having traversed the nerve-ring, passes forward towards the 
anterior end of the carapace. Here it enters into a somewhat 
> shaped and spacious proventriculus; posteriorly the proventri- 
culus opens by a funnel-shaped valve into the anterior end of the 
narrow intestine. All these structures are derived from the 
stomodaeum, are lined with chitin and are provided with very 
muscular walls whose internal surface is thrown into longitudinal 
ridges. The intestine runs straight backward, diminishing in its 
diameter, and ends in a short, chitin-lined, and muscular rectum 
which is derived from the proctodaeum ; the anus is a longitudinal 
shit. A large gland, usually called the liver, consisting of in- 
numerable tubules, pours its secretions into the broader anterior 
end of the intestine by two ducts upon each side; it extends 
into the meso- and meta-soma, and, together with the repro- 
ductive organs, forms a “packing ” in which the other organs are 
embedded. The contents of the alimentary canal are described as 
“pulpy and scanty,” and probably much of the actual digestion 
goes on inside the lumen of the above-mentioned gland. 
The vascular system of Limulus, like that of the Scorpions, is 
more completely developed than is usually the case in Arthro- 
pods. For the most part the blood runs in definite arteries, and 
when it passes as it does into venous lacunae these are more 
definite in position and in their retaining walls than in other 
members of the phylum. 
The heart les in a pericardial space with which it communi- 
cates by eight * pairs of ostia. Eight paired bands of connective 
tissue, the “alary muscles” of authors, sling the heart to the 
' A rudimentary ninth pair of ostia are described anteriorly. 
