214 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



generations of unicellular organisms derived from one another by a 

 continuous course of simple division into two. 



The author divides his essay into three chapters, the first of 

 which deals with the germ-plasma. Fecundation is regarded as the 

 union of the nuclear substance of the maternal and paternal individual 

 but this substance is not the same as Nageli's idioplasm, for it does 

 not extend through the whole body. The view is discussed and 

 support for it drawn both from the animal and the vegetable kingdom. 



In the second chapter a new theory of the meaning of the polar 

 vesicles is advanced ; their extrusion is regarded as the getting rid of 

 histogenetic plasma, in order to leave the germ-plasma free to act ; 

 it is, in fact, the removal of ovogenous nucleo-plasma. The third 

 chapter treats of parthenogenesis, and in a postscript to it the dis- 

 covery of a polar vesicle in the parthenogenetic summer eggs of 

 DaphnidaB is announced ; this strikes at the root of Balfour's theory, 

 and an explanation of parthenogenesis must be looked for in the 

 quantity of contained germ-plasma ; when there is a certain mass the 

 segmentation nucleus proceeds to the process of ontogenesis ; in the 

 ordinary sexual process it is the increase of the nucleus which gives 

 the stimulus to segmentation, the disposition to which was there 

 already. " Sperm-nucleus and egg-nucleus do not differ in their 

 nature," and in certain algse Von Berthold has discovered not only a 

 " female, but also a male parthenogenesis " {Ectocarpus, Scytosiphon). 

 It can hardly be doubted that conjugation is the sexual reproduction 

 of unicellular organisms. 



Attack and Defence as Agents in Animal Evolution.* — Mr. C. 



Morris thinks he perceives four successive ideas emerging into 

 prominence in the development of the animal kingdom. In the 

 primeval epoch it is probable that only soft-bodied animals existed, 

 when the weapons of assault were the tentacles, the thread-cell, the 

 sucking-disc, and other unindurated weapons. At a later period 

 armour became generally adopted for defence, and the tooth became 

 the most efficient weapon of attack. Still later, armour was discarded 

 and flight or concealment became the main method of escape, and 

 swift pursuit that of attack, while claws were added to teeth as 

 assailing weapons. Finally, mentality came into play, intelligence 

 became the most efficient agent in both attack and defence, and a 

 special development of the mind began ; this has found its culmina- 

 tion in man, side by side with whom we have in existing conditions 

 of life an epitome of the whole long course of evolution. 



j3. Histology.f 



Cells of the Epidermis of Batrachian Larvse.f — Prof. F. Leydig 

 thinks that the cells lately described by Kolliker § as being provided 

 at their free end with fine processes, are the same as what are already 



* Proc. Acad. Nat. Sci. Philad., 1885, pp. 385-92. 



t This section is limited to papers relating to Cells and Fibres. 



X Zool. Anzeig., viii. (1885) pp. 749-51. 



§ See this Journal, v. (1885) p. 977. 



