INVERTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 697 



doctrine of evolution. He adopts the classification of teeth pro- 

 posed by Cope, and endeavours to explain by mechanical laws the 

 jihylogeuy of the various existing dental types pointed out by the 

 same author. The ai>plication of mechanical theory to this question 

 is ingenious, and results in some very probable hypotheses. First 

 among these is the supposed effect of lateral pressure in flattening 

 conical cones or cusps, so that their section becomes semicircular or 

 crescentic. Another is the probable crowding of tubercles on each 

 other by impact transverse to their directions, producing plicate 

 structure. 



A summary of his views is stated by the author as follows : — 



1. The earliest and simplest type of mammalian jaw-movement was 

 that in which the mouth was simply opened and closed, without 

 mandibular excursion, and co-existent with the simple haplodont or 

 binodont molar. 



2. The development of the various kinds of excursion mandibular 

 movement has apparently been progressive. 



3. As the excursive movements have increased in complexity, 

 there has been an apparent increase in the complexity of the enamel 

 foldings, ridges, and crests. 



4. From the fact that the foldings, &c,, have apparently been 

 modified in conformity to the ways in which the force used in 

 mastication was exerted, it is concluded that the various modes of 

 crest and tubercular modification are related as effects to the diverse 

 modes of mandibular movement. 



5. It is apparent from the facts presented throughout the context 

 that the mandibular articulations, and correlatively the skull, have 

 probably been modified in shape by the movements made by the jaws 

 and the forces exerted in executing them. 



6. From the fact that the incisor teeth are partially or entirely 

 absent, or relegated to another function, in forms which have long 

 prehensile tongues, mobile, prehensile lips or proboscides, it is held to 

 to be probable that such disappearance of the incisive dental elements 

 is due to the assumption of their function by the prehensile organs 

 indicated. 



Refractive Powers of Animal Tissues.* — We can only draw 

 attention to the very valuable results attained by Professor Valentin, 

 in which the ordinary blood, the menstrual blood, and the blood of the 

 umbilical vein of man are examined, as well as those of a large 

 number of animals ; with these are connected a series of observations 

 on the blood-corpuscles, on the influence of coagulation, and on the 

 characters of the serum. The bile is also examined, as is the urine 

 and the sperm ; milk and other fluids, as well as albumen, are tested, 

 while the brain itself, the lens, and muscular fibre did not escape 

 examination. 



Innervation of the Respiratory Organs. — The fourth number 

 of the 47th volume (1879) of the ' Bull, de I'Acad. Eoy. de Belgique' 

 contains a memoir by Dr. Fredericq on this subject, together with a re- 

 * Pfliiger's ' Archiv,' xix. (1870) p. 78. 



