ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 171 



centre differ less or more widely from the type as they approach 

 nearer the boundary of the species. As a species moves, either in 

 geographical space or geological time, the position of its centre will 

 gradually alter, if its environment be different, so that forms like those 

 contained near the boundary of the species A, and therefore not typical 

 of it, may become the centre of the species B and typical of it. These 

 sentences give a general indication of the author's point of view. 



Theory of Sleep.* — A. Gorter begins by discussing the different well- 

 known theories as to the cause of normal sleep. Sleep has been referred 

 to "anaemia of the brain," to interruption" of contact between the neura, 

 to accumulation of fatigue-substances, and so on. G-orter thinks that 

 normal sleep is due to cessation or decrease of stimuli from the sur- 

 roundings, and that it has been phylogenetically evolved in direct 

 relation to the sun. Man's need for sleep is an inheritance from the 

 animal world, and may be greatly lessened. In coming generations 

 sleep may perhaps be dispensed with, but the individual life will be 

 shortened. 



Nutritive Arteries of Long Bones. f— P. Piollet finds that in 

 human embryos the principal feeding arteries of the long bones of 

 the limbs are either perpendicular, or inclined towards the distal 

 extremity of the limb, i.e. in the direction of the blood current. As 

 growth goes on, by the fact of unequal growth at the two extremities of 

 the bone, the place of entrance of an artery into the bone is carried 

 away from the epiphysis which furnishes most of the bone. The result 

 is, the feeding artery takes an oblique course and is directed to the 

 extremity of the bone which is growing least. In consequence of growth 

 in fchicknesn, by the juxtaposition of osseous layers of periosteal origin, 

 the nutritive canal also takes the same obliquity. In adults the feeding 

 arteries and the canals containing them are directed as follows : For 

 humerus, radius and ulna, towards the elbow ; for femur, tibia and fibula, 

 from the knee ; for metacarpals and metatarsals, towards the extremity 

 without uniting cartilage. Briefly, the nutritive arteries of the long 

 bones of the adult are directed away from the more active epiphyses, the 

 mechanical result of the unequal elongation of the two extremities of 

 the bone. 



Multiple Origin of Horses and Ponies. $ — J. Cossar Ewart points 

 •out that in post-glacial as in pre-glacial times there were several distinct 

 species of horses, and that it is extremely probable that some of the pre- 

 historic species and varieties have persisted almost unaltered to the 

 present day. He describes three distinct kinds of living horses, viz. the 

 wild horse of the Gobi desert {Eguus caballus prjevalskii) ; the Celtic 

 pony, which, though no longer wild, may be known as Equus caballus 

 celtieus ; and the Norse horse, which may very well stand as the type of 

 the large occidental breeds and be known as Equus caballus typicus. 



In addition to these three very distinct types — two at least of which 

 have taken part in forming quite a number of our British breeds — we 



* K. Akad. Wetenschappen Amsterdam (Proc. Sect. Sci.) vi. (1903) pp. 86-91. 



t Journ. de PAnat Phys., xli. (1905) pp. 40-57. 



X From Trans. Highland and Agric. Soc. Scotland (1904) 39 pp. (25 figB.). 



N 2 



