ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 245 



It may be said that the hypophysis of Holocephali corresponds in 

 the main to the perimeningeal portion of the hypophysis of Selachii. 

 The hypophysial sac appears to arise as an outgrowth from the buccal 

 ectoderm. 



Posterior Upper Incisors of Rabbit.* — Chiavaro has made a study 

 of the small incisors which lie behind the front upper incisors in the 

 rabbit and other Duplicidentata. The result of his inquiry is the con- 

 clusion that these teeth function in mastication (the lower incisors biting 

 against them), and that they also serve to protect the peridental mucosa 

 of the palate. Chiavaro thinks that they are analogous in function to 

 the cingulum and to the fifth cusp iu human dentition. 



Venous System of Dogfish.f— Chas. H. O'Donoghue has given an 

 exceedingly careful description of the venous system of Scyllium canicula, 

 of which a complete account was needed. He deals with the develop- 

 ment in later embryos of 37 and 56 mm., and with the adult condition. 

 The characteristic dilatation of the venous system to form sinuses 

 renders the task a very difficult one. 



Radiogenesis in Evolution. J — Heber A. Longman argues that 

 variations have arisen " not definitely and simply, but polychotomously." 

 The key to the process has been ' ; radiogenesis," and not orthogenesis. 

 He refers to such " radial variation " as is to be seen in the Drepanidse 

 of the Hawaiian Islands, in the land snails of Oahu, and in the marsupials 

 of Australia. 



Tunicata. 



Self-sterility in Ciona.§ — E. M. East discusses the self-sterility 

 (the practical impossibility of self-fertilization) discovered by Castle 

 (1896) in Ciona intestinalis, and well known in some plants. Under 

 uniform suitable conditions, individuals of Ciona vary in degree of self- 

 sterility, it being exceptional to find an animal that is perfectly 

 self-sterile. Self-fertility has never equalled cross-fertility, though the 

 possibility remains that some animals may be self -fertilized as easily as they 

 may be crossed with certain particular individuals. The ease with 

 which the ova of any animal " A " may be fertilized by the sperm of 

 other individuals may vary. A chemical basis for self-sterility is shown 

 in Fuchs's experiments, by (a) the decrease in ease of cross-fertilization 

 after contact of ova with sperm from the same animal, and by (b) the 

 difference in ease of cross-fertilization after various artificial changes in 

 the chemical equilibrium of the medium surrounding the ova. r». 



From his studies on fertilization in flowering plauts, East concludes 

 that the secretions in the style offer a stimulus to pollen- tubes from 



* Atti (Rend.) R. Accad. Liucei Roma, xxiii. (1914) pp. 29G-302 (7 figs.), 

 t Proc. Zool. Soc. London, 1914, pp. 435-55 ( 2 pis. and 4 figs.). 

 J Proc. R. Soc. Queensland, xxvi. (1914"> pp. 23-39. 

 § Amer. Nat., xlix. (1915) pp. 77-S7. 



