ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 399 



wide-spread genus Peachia are all medusophilous, and that the single 

 deep siphonoglyph, possessing as it does an opening below the 

 oesophageal folds, is a larval organ correlated with the parasitic habit. 



Conducting; Paths in Ctenophores.* — C. M. Child has studied 

 Mnemiopsis leidyi, in which, though a morphologically differentiated 

 nerve has not as yet been found, there seems to be a passage, from the 

 apical region oralwards, underneath the ciliary plates, of an impulse 

 resembling a nerve impulse. An inquiry has been made into the 

 existence of a gradient in metabolic rate or in rate of oxidation along 

 the plate-row, with its highest point at the apical or aboral end. It is 

 found that there is such a gradient in susceptibility to KCX. 



The gradient is indicated by the fact that decrease in amplitude of 

 vibration, increase in rhythmic period, and cessation of rhythmic move- 

 ment occur first at the aboral end of the plate-row, and show a regular 

 progression toward the oral end. Since the plates remain capable of 

 responding to direct mechanical stimulation by beats of full amplitude 

 after the rhythmic beat has ceased, decrease in amplitude and cessation 

 of rhythmic movement must be due primarily to changes in the trans- 

 mitted impulse rather than in the plates themselves. 



This susceptibility gradient is an indicator of a gradient in general 

 metabolic rate and in protoplasmic conduction associated with it. 

 According to the relation between susceptibility and general metabolic 

 condition the aboral end of the plate-row is the region of highest 

 metabolic rate in this gradient, and from this the rate decreases in the 

 oral direction. Many details are given in regard to this " physiological 

 axis," which is fundamentally similar in behaviour to the main body 

 axes of other organisms. These are also in their simplest terms 

 metabolic gradients. The experimental data serve as a basis for con- 

 sideration of the general significance of metabolic or dynamic gradients 

 as physiological axes, both in the organism as a whole and in its parts, 

 even in axes so highly specialized as nerve fibres. 



Protozoa, 



Affinities of Entamoeba.! — C. Mathis and L. Mercier have made a 

 detailed comparative study of Entamoeba Jegeri Mathis from Macacus 

 rhesus and Entammha coli from man. They compare the vegetative 

 forms, the development of the cysts, and the division, and show that the 

 agreement is very close. Certain differences in the nucleus and mode of 

 division seem to warrant the separation of the two species. In both the 

 first phase in division is a mesomitosis, but E. hgeri shows in each half 

 of the dividing nucleus a large chromatic body which arises from a 

 fusion of chromatin granules, and persists for some time in the nuclei 

 of the young amoebaj, first reniform, then like a crescent, then like a 

 horseshoe. This is not seen in E. coli. 



* Amer. Journ. Physiol., xliii. (1917) pp. 87-112. 



t Arch. Zool. Exper., Ivi. (1917) Notes et Rr- ue, No. 3, pp. 63-72 (4 figs.). 



