ASCARIS. 203 
ventral, and lateral—and consisting of a protoplasmic matrix. 
without distinct cell-limits. Except at the tail-end the 
nuclei are confined to the longitudinal lines, and are most 
numerous laterally. The epidermis makes and remakes. 
the cuticle, which is periodically moulted. (¢) Beneath the 
epidermis is a layer of remarkable muscle cells, lying in 
groups defined by the lines mentioned above. Many of 
the Nematodes are very 
agile. 
Around the pharynx there 
is a nerve-ring from which 
six nerves run forwards and 
six backwards. One runs 
along the median dorsal 
line—a unique position in 
an Invertebrate. Here and 
there on the ring and on the 
nerves there are ganglionic 
cells, but there is but little 
aggregation of these into 
ganglia. Sense organs are 
represented by the papillze 
already mentioned. 
As the food consists of 
juices from a living host, 
it is not surprising to find py, 106, Cross-section through 
that the alimentary canal Ascaris. 
has but a narrow cavity. azx., Dorsal nEEvE aie non-contractile 
. a portion of muscle cells; ¢., cuticle; ¢. 
It consists of three parts epidermis; 2.2, lateral line; 0.5, ex. 
a fore-gut or cesophagus, erStory. vessel Me, cee portion of 
: . s 3 Utes tra 3 
lined bythe inturned cuticle, Qury; uz, uterus;g, gue 
a mid-gut or mesenteron of 
endodermic origin, and a usually short hind-gut or rectum 
lined by the cuticle. When the external cuticle is shed, so 
is that of the fore-gut and hind-gut (cf. Crayfish). 
There is a distinct space between gut and body wall, but it is lined 
externally by the muscle cells, internally by the endoderm of the gut, 
which has no mesoblastic coat; the space is therefore not strictly 
ccelomic. It contains a clear fluid, which probably discharges some of 
the functions of blood. There are xo free amaboid phagocytes. 
Embedded in each lateral line there is a longitudinal canal. These 
