176 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
y. Gastropoda. 
Origin and Development of Central Nervous System in Limax 
maximns.* — Miss Annie P. Henchman, who has made a study of this 
subject, has arrived at the following conclusions. The whole of the 
central nervous system arises directly from the ectoderm. The cerebral 
g ingli . i ' iris is a j di : true i .v - 
the body in front cf the pleural groove and behind and below the bases of 
the ocular tentacles. During development the neck of each invagination 
becomes a long, narrow, tube-like structure, which remains open 
throughout the period of embryonic life. The chief part of these 
ganglia is formed from cells which are detached at an early period from 
the deep ends of their cerebral invaginations, or from adjacent ectoderm ; 
the portions which persist as the walls of the infoldmgs finally form 
distinct lateral lobes of the brain. 
All the other ganglia originate by cell-proliferation from the 
ectoderm without invagination. The ganglia arise separately, and with 
the exception of the abdominal and pallial ganglia, in pairs, one on 
either side of the body. They become connected with each other by the 
outgrowth of nerve-fibres. 
In advanced stages the central nervous system consists of five pairs of 
ganglia and an azygous ganglion, which together form three complete 
rings surrounding the oesophagus. 
If a series of sections be examined from behind forwards there are 
first seen the paired pedal ganglia, which lie under the radular sac, and 
are joined to each other by an anterior and a posterior commissure. 
Behind these there is an abdominal ganglion, which lies a little to the 
right of the median plane. A pair of visceral ganglia occupies the 
posterior angle formed by the outgrowth of the radular sac from the 
oesophagus; they are separated by the abdominal ganglion, whence 
connectives pass to them. There then follows a pair of pleural ganglia 
which are not joined by a commissure, and do not give off nerves ; they 
are only united by means of connectives to the pedal, visceral, and 
cerebral ganglia of their own sides. Next in front comes a pair of 
ral ganglia with their supra-cesophageal commissure, and with con- 
nectives to the pleural, pedal, and buccal ganglia. And, lastly, there is 
a pair of buccal ganglia. 
The paper concludes with a critical notice of the work of preceding 
observers. 
Pericardial Gland of Gastropoda.j — Prof. C. Grobben gives an 
account of the pericardial gland, which is found in so many Gastropods ; 4 
it is derived from the epithelium of the secondary body-cavity, and is 
closely connected with the blood-vascular systems. After describing 
the anatomical details of the ergan in various Gastropods belonging to 
different groups, the author points out that the relations of the organ to 
the blood-vascular system are very similar to those which obtain in 
Cephalopods and Lamellibranchs ; but the epithelial cells are nearly 
always flat, and no striation or formation of concretions is to be 
observed. Although, therefore, there is no evidence from the structure 
* Bull. Mus. Comp. Zool., is. (1>90) pp. 169-208 (10 pis.), 
t Arbeit. Zool. Inst. Wien, is. (1890) pp. 35-56 (1 pi.). 
