166 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the head, the ganglia and their relation to the ectoderm, and the 

 histogenesis of the nerves. He has also some notes on the sensory 

 lines in Torpedo. These arise as straight parallel-walled tubes, upon 

 which lateral swellings develop on one side. These later reach the 

 surface as open lateral tubules. Nerve-bulbs are situated opposite the 

 points of origin of these side tubules. They are without doubt sensory 

 structures, which in the course of phylogeny have arisen from corre- 

 sponding structures situated on the surface. 



Hardening of Teeth Enamel in Man.* — V. v. Ebner has studied 

 the changes in enamel during hardening. As a rule, hardening takes 

 place slowly, and is effected by a fluid stream (Saftestrom) of dentine 

 into the inter-prismatic cement substance. The typical Retzius lines 

 — contour lines — occurring in persistent teeth, as also the contour bands 

 in milk-teeth, are due to a stoppage in the development of the enamel 

 at an early stage of its growth. The formation of the enamel prisms 

 stands in a much closer relation to the vital activity of the enamel cells 

 than the formation (in many respects similar) of the prism layer of the 

 mussel shell to the epithelial cells of the mantle edge. The typical 

 arrangement and direction of the prisms are due to an inherited self- 

 differentiation of the enamel cells ; on the other hand, the form of the 

 prisms seen in cross section admits of a mechanical explanation. 



Red Blood Corpuscles of Amphibia. — F. Meves f gives an account 

 of various alterations of form undergone by the red blood cells of 

 frog and salamander when exposed to ammonia fumes and solutions. 



J. Dogiel,+ also, shows that under the influence of various physical 

 and chemical agents, the form and composition of the red blood 

 corpuscle may vary. Some indication also of the possibility of artificial 

 initiation of mitosis of these and other tissue-elements has been found. 



The Haemocoele Theory.§ — F. Vejdovsky has investigated the re- 

 lations of the vascular system in the Enchytrseidte, and in the light of 

 the facts elucidated discusses the haeruoccele theory. To the question as 

 to whether the hsemoccele is a remnant of the original blastoccele, or is 

 an extra-intestinal mesoblastic schizoccele, he gives the following answer. 

 The vascular system cannot be traced to the blastoccele ; its most 

 primitive constituent part, viz. the gut sinus with its outer cellular 

 boundary, is an integral part of the endoderm. Neither can it be 

 explained as schizoccele (in Huxley's sense), because it does not arise in 

 the mesoblast ; the mesodermal muscular layers represent a secondary 

 envelope upon an endodermal structure. It is, in fact, a cavity sui 

 generis, only fittingly distinguished as hasruoccele, which, nevertheless, is 

 no new formation, since its original constituents — the blood-fluid and 

 the enclosing vasothelium — arise from the endoderm. 



Life-History of Blennius pholis.|| — W. C. Mcintosh describes the 

 egg, which possesses a disk for adhesion, and gives particulars of growth 



* Arch. Mikr. Anat., lxvii. (1905) pp. 18-81 (4 pis.). 



t Anat. Anzeig., xxvii. (1905) pp. 177-86 (17 figs.). 



X Zeitschr. wiss. Zool., lxxxii. (1905) pp. 171-81 (1 pi.). 



§ Tom. cit., pp. 80-170 (5 pis.). 



|| Op. cit.. lxxxvi. (1905) pp. 368-78 (1 pi.). 



