2 SCIENCE PROGRESS: 
Haller and Boutan; Bouvier has thrown new light upon the 
Opisthobranchia by his researches on Acteon ; Boas and 
Pelseneer have revolutionised our ideas of the Pteropoda 
by their work upon Lzmacena among the Thecosomata, and 
upon Dexiobranchea and other types among the Gymnoso- 
mata ; the morphology of the Pelecypoda has been further 
elucidated by Pelseneer’s observations upon Vucu/a and 
other primitive forms, and important contributions to our 
knowledge of the Cephalopoda were made during the past 
year by Huxley and Pelseneer in the case of Spzrula, that 
last survivor of the ancient types of Decapod Dibranchiates. 
We doubt if any equivalent group of the animal kingdom, 
except perhaps the Echinoderma, has been the subject of 
such productive researches as the Mollusca during the period 
under consideration ; and certainly the phylogenetic method 
of inquiry has attained no greater triumphs than in the 
hands of Bouvier, Haller, Pelseneer, and other inves- 
tigators of the Gastropod and Lamellibranch series. 
In the present article | propose to deal more especially 
with recent contributions to our knowledge of the Molluscan 
nervous system, reserving a fuller consideration of other 
questions for a later article. 
There is one writer, however, whose views must first of 
all be dealt with, as on a great number of fundamental 
points they are opposed to all current conceptions of 
Molluscan morphology. These views merit some detailed 
consideration, moreover, for they are based on propositions 
which are not without a certain appearance of plausibility, 
and may well serve as test-questions by which to examine 
into the accuracy of the homologies which have been 
generally admitted to exist between the different sections 
of the Molluscan phylum. 
Thiele has published his views in a series of lengthy 
papers, the references to which will be found in the biblio- 
graphy (23, 24, 25). He regards the Mollusca and Anne- 
lida as direct descendants of Polyclad Turbellarians, and 
