ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 413 



strongly marked. In ruminants these arise, while the primitive kidneys 

 are present in the cranial region, from the lateral borders of the same ; 

 in other mammals they spring from the dorsal body wall. The relations 

 of the developing rumen to the lungs, liver, and diaphragm are described 

 as is also the mechanism of the " turning " of this region of the stomach 

 spoken of by Martin. 



b. Histolog-y. 



Minute Structure of Parietal Eye in Lacerta and Anguis.* — 

 M. Nowikoff has studied the parietal eye in adults of Lacerta agilis 

 and Anguis frag His. He has directed his attention especially to the 

 following points : — the nervous connection between the parietal organ 

 and the brain ; the relation of the definitive nerves to the sensory 

 cells ; and the structure of the retina. 



Intercellular Bridges of Gut Epithelium.-j- — T. Schaeppi describes 

 these in the gut of frog and mouse. They are protoplasmic strands 

 connecting the epithelial cells across the intercellular lymph spaces. 

 They vary in thickness and are contractile, and assist the wandering of 

 the epithelial cells. Another significance attached to them is that of 

 effecting a nervous rapport between the epithelial cells. Since, for 

 example, only certain of the gut cells are directly connected with the 

 nerve-endings, it is natural to suppose that the secretion-impulses are 

 transmitted to the other epithelial cells by means of intercellular bridges. 



Symbiosis.^ — A. Famintzin starts from the fact that lichens show 

 a symbiosis of fungoid and algoid organisms. He regards this as a 

 synthesis of autonomous higher organisms from two kinds of simpler 

 organisms. He asks whether there are not many similar cases ; whether 

 the green plant-cell in general does not illustrate symbiosis ; whether 

 bacteria are not normal symbions in many cases ; and so on. His idea 

 is that symbiosis of lichens may give us a useful clue in the analysis 

 of organisms in general, leading us perhaps nearer the elementary 

 vital units, and suggesting possible syntheses, after the example of the 

 chemists. 



c. General. 



Migration of Birds.§ — H. Duncker gives a critical review of re- 

 searches and opinions on this subject, from Aristotle to the present day. 

 His own chief conclusions on the matter are stated thus : — " The 

 tracks followed by the birds are, on the whole, distribution routes. 

 Prolongation and abbreviation give the length of the distribution, 

 deviation the direction. The centre of distribution is not to be 

 discovered from the tracks alone. The route north of the centre is to 

 be regarded as the ' Sommerfrischlerabschnitt,' the route south from 

 the centre as the ' Winterfliichterabschnitt.' The centre of distribu- 

 tion is liable to alter. By prolongation resident birds have become 



* Biol. Centralbl., xxvii. (1907) pp. 364-70 (5 figs.), 

 t Arch. Mikr. Anat., Ixix. (1907) pp. 791-806 (1 pL). 

 X Biol. Centralbl. xxvii. (1907) pp. 353-64. 



§ Wanderzug der Vogel. Jena : G. Fischer, 1905, 118 pp. See .also Zool. 

 Centralbl., xiv. (1907) pp. 279-80. 



