ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 417 



Plasticity of Organisms and Evolution.* — M. M. Metcalf dis- 

 cusses the influence of plasticity, or individual adaptability, on the 

 course of evolution. A high degree of plasticity hinders evolution by 

 selection, since those congenitally modified in the direction of adaptation 

 have little advantage over those " ontogenetically " adapted. Plasticity 

 may, however, preserve a species in time of stress, till an advantageous 

 trend is established. 



Image-forming Power of Various Eyes.f — L. J. Cole tested in an 

 elaborate manner the reactions of certain animals to two sources of light 

 equal in intensity but differing in area, one being a surface, the other a 

 point. He found that Vanessa antiopa, Ranatra fusca, and two species 

 of frogs, Acris gryllus and Rana damata, all of which are positively 

 phototropic, turned more often to the large luminous surface than to the 

 point source, being able evidently to distinguish between the two lights. 

 He inferred that the eyes of these animals possess a certain power of 

 forming an image. Bipalium Jce/vmse, Oniscus aseUus, Tenehrio molitor 

 (larva), and Periplaneta americana, turned as often from the one light 

 as from the other, reacting only to intensity of stimulus, not to size of 

 image. These are all negatively phototropic. AlMobophora fivtida and 

 a blinded frog were also indifferent in their reaction, the worm being 

 negatively, the frog positively, phototropic. All these reactions are 

 correlated with the natural habits of the animals. 



Equilibration and the Semicircular Canals. | — L. Bard maintains 

 that the functioning of the sense of equilil)ratiug orientation is exactly 

 comparable to that known for sight in connection with the optic chiasma, 

 and revealed also in pathological hemianopsia. In connection with 

 hearing also there is a physiological chiasma. 



Tunicata. 



Endostyle of Appendiculari8e.§ — J. E. W. Ihle has studied the 

 somewhat complex endostyle in Megalocercus huxleyi, and compared it 

 with the simpler type in Oikopleura dioica and other species, and the 

 still more reduced type in Fritillaria pellucida. In Koivalevskia the 

 whole endostyle has disappeared. A careful comparison shows that the 

 endostyle of Megalocercus is closely homologous with the endostyle of 

 Ascidians, with its three pairs of glandular zones and three pairs of 

 ciliated streaks. The median streak of ciliated cells in the Ascidiau 

 endostyle is absent in Megalocercus, but otherwise they are much the 

 same. The conclusion drawn is that the endostyle of Appendicularias is 

 not a starting point for the Ascidian endostyle, but is rather a reduced 

 form of it. It is true that the Appendiculari^ retain some primitive 

 features, but they are in other respects specialised for pelagic life, and 

 one of their lines of evolution has been a reduction of the endostyle. 



* Science, n.s., xxiii. (1906) pp. 786-7. 



+ Proc. Amer. Acad. Arts and Sci., xlii. (1907) pp. 335-417 (.ll figs.). 



J Arch. Sci. Phys. Nat., xxiii. (1907) pp. 91-3. 



§ Zool. Anzeig., xxxi. (1907) pp. 770-6 (1 fig.). 



