110 
Prof. Carl Claus on the 
in the form of bacilli on the visual cells of Gypridina , which 
are turned towards the pigment, but within, turned towards 
the pigment, 1 have found a second layer of narrow elongated 
nuclei, which must belong to a special form of cells. The 
rounded nuclei of the nerve-cells are placed peripherally, 
turned towards the entering nerves and the overlying secre- 
tion-lens, which is clothed by the delicate integument. In 
Notodromus the three divisions of the frontal eye are sepa- 
rated from each other, and here, as in the Pontellce and Onis- 
cidice among the Copepoda, we have an anterior, ventral, cup- 
shaped eye and two separated lateral eyes, which are easily 
distinguished from the composite lateral eyes. 
3. Endoskeleton, — Beneath the oesophagus, between the 
stomach and the anterior ganglionic mass of the ventral cord, 
in front of the transversely placed sinew of the shell-muscle, 
there is a broad, indistinctly bipartite, chitinous plate, upon 
which, in agreement with the endoskeleton of the Phyllopoda 
and other Crustacea, as also with the so-called endostomite of 
the Arachnoidea, pairs of muscles for all the limbs of the 
trunk, including the second pair of antennse, are attached. 
On its anterior margin originate numerous muscular threads, 
which pass to the lower wall of the oesophagus, and two slender, 
long, muscular bundles, which pass through the space between 
the mandibular and maxillary ganglia to the labium. 
4. The alimentary apparatus commences by a rather nar- 
row atrium, bounded by the labrum and labium, into which 
the toothed biting edge of the mandibles enters from the right 
and left. Zenker’s u rake-like masticating organs ” are 
situated at the bottom of it, and belong, as a sort of hypo- 
pharynx, to the labium. In the bottom of the atrium beneath 
the labrum commences the buccal intestine, ascending at 
first nearly perpendicularly and then somewhat obliquely 
backwards to the stomach. The shorter anterior part of it 
(oesophagus), which is about equal in length to the atrium, 
appears to be nearly cylindrical, but with a more strongly 
arched ventral wall, into which the pair of muscles springing 
from the endoskeleton and acting as dilaters enter. More 
numerous and larger muscles pass from the integument of the 
labrum to the flattened dorsal surface of the oesophagus, and 
draw up its very thick wall, the convex surface of which 
projects like a valve into the lumen, and thus, in conjunction 
with the dilaters of the lower oesophageal wall, enlarge the 
lumen, which is horseshoe-shaped in transverse section. The 
following larger division of the oesophagus (gizzard) appears 
to be essentially altered in form ; it was described by Zenker 
as a very complicated triturant organ, resembling the human 
