1891.] Some Recent Papers on Earthworms. 3 
coelomic cavities are schizoccelia, and are formed in the mesodermal 
bands behind the point of concrescence; the most anterior pair 
lie at the sides of the stomodzum, while a head cavity, which is 
always unpaired, occurs in front of the mouth. 
The first blood vessel to appear is the subintestinal. It is at 
first without proper walls, and is apparently a remnant of the 
cleavage cavity. The dorsal vessel is at first double. The two 
halves concresce from in front backwards. 
Concerning the alimentary canal little need be said in this ab- 
stract. The stomodzum pushes inward as far as the sixth seg- 
ment, and in one species its lips are at one time armed witha 
peculiar structure which may be either sensory or may serve as a 
larval digestive organ. As soon as the stomodzum is formed the 
larva begins to swallow the albumen with which it is surrounded 
and the particles of this are apparently swallowed amceba-like by 
the entoderm cells. The cesophagus with its calciferous glands 
is entodermal. The proctodzeum is long delayed, and when it 
appears it is formed in the region where the primary mesoblasts 
break up; but our author was not able to decide whether in front 
or behind them, t.e., within or without the limits of the blastopore. 
The nervous system arises from the neural rows budded from 
the neuroblasts. The two most important statements made are: 
that the brain arises from these rows, and that it has a primitively 
paired condition and does not arise from a scheitelplatte. Dr. 
Wilson was unable to find any mittelstrang in the ventral cord. 
With growth the brain is carried backward from an extreme 
anterior position to the third somite, while by the same process 
the ganglia of the two anterior pest-oral somites are pushed back 
upon that of the third to form the infracesophageal ganglion. 
The giant fibres are apparently specially modified nerve fibres,—a 
view in conflict with Vejdovsky’s account. 
The origin of the excretory system as described by Wilson is 
quite different from the accounts of Bergh summarized farther on. 
First in the history comes the larval excretory organs or “ schluck- 
zellen,” which are at first large ectoderm cells forming the anterior 
lip of the blastopore, and connected with a delicate system of 
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+ 4. 
Y it 55S Y FCM. 
