62 Miscellaneous. 



gcologicnl periods. Some indications have been offered in the 

 course of the essay, as shown above. The Mesozoic floras in par- 

 ticular have j'et to be carefully reviewed as tests of climate. Sug- 

 gestive remarks on fossil Ferns and Conifers are then offered ; and 

 the Author says : — " We may expect that a closer study of the 

 Geological floras, not only from pliylogenctic and anatomical, but 

 also from biological points of view may enable us to penetrate further 

 into the life-conditions of those forests of which the Earth's crust 

 affords us such numerous, though often too fragmentary, relics." 



Tlie list of works referred to in the text, occupying pages 134- 

 1-1(3, well arranged and made serviceable with reference to the 

 numerous footnotes, is a welcome bibliography for palaeobotanists. 

 The Essay has also a useful Index. Like other scientific works 

 issuing from the University Press at Cambridge, this is well printed 

 on good paper. 



MISCELLANEOUS. 



Comparative Researclies upon tlie Organization of the Brain in the 

 principal Groups of Arthropods. By M. H. Viallanes. 



I HAVE the honour of conimuuicating to the Societe de Biologic 

 the principal results of researches which I have been conducting for 

 several years upon the organization of the nervous system of 

 Arthropods, and of which 1 have hitherto only published detached 

 fragments, some in the ' Annales des Sciences iS'aturelles ' and the 

 rest in the ' Comptes Bendus do I'Academie des Sciences.' 



Organization of the Brain of Insects. — In the Insects the brain is 

 formed of three segments corresponding to the first three cephalic 

 zonites. The first segment, or j)>'Otocerebron, innervates the eyes ; 

 it is the seat of the visual perceptions, while the psychic centres also 

 reside in it. The second segment, or deutocerebron, innervates the 

 antennfe ; it is the seat of the olfactory perceptions. The third 

 segment, or tritoccrehron, innervates the labrum and the initial 

 portions of the digestive canal ; in it is situated the centre of the 

 gustatory sense. 



Before entering further into detail as to the constitution of the 

 cerebral segments, it may be mentioned that the first two are 

 entirely preoesophageal, that is to say that the commissures which 

 unite their symmetrical portions are situated in front of the 

 oesophagus. In the case of the third segment the conditions are 

 different ; here all the commissural fibres pass behind the oeso- 

 phagus, where they constitute the commissure known under the 

 name of the transverse comndsszire of the oesophagecd ring. 



The protocerebron is composed of a pair of lateral masses termed 

 optic ganglia and of an intermediate median mass. The constitu- 

 tion of the optic ganglia is most remarkable and most constant ; 



