ZOOLOGY 381 



oesophageal ganglion. The adult condition in Peripatus is, 

 then, an embryonic stage in the Myriapoda. 

 Other important papers are : 



Evans, T. J., " Calma Glaucoides : A Study in Adaptation," Q.J. M.S., 



vol. Ixvi, Part III, Sept. 1922. 

 Hilton, W. A., " The Nervous System of Phoronida," Jr. of Comp. Neur., 



vol. xxxiv. No. 4, Aug. 1922. 

 Seidler, H. J., " Beitrage zur Kenntis der Polynoiden, 11," Zool. Am., 



Bd. Iv, Nos. 3, 4. 



Experimental Zoology of Planarians. — " The Control of Head- 

 formation in Planaria by Means of Anaesthetics " is the subject 

 of an investigation by J. W. Buchanan {Jr. of Expt. Zool., 

 vol. xxxvi, No, I, July 1922). Experiments conducted with 

 headless pieces of Planaria showed that the factors controlling 

 head-formation are non-specific, and strongl}'- support Child's 

 conclusion, i.e. that head-formation is determined chiefly by 

 the relative activities of two antagonistic factors, viz. : 



" (i) The tendency of the cells near the anterior cut surface 

 of the piece to de-differentiate and develop into the head of 

 the new individual ; and (2) the tendency of the whole piece, 

 exclusive of the cells directly concerned in the development 

 of the new head, to maintain the differentiation of the old 

 individual. This region exerts a certain degree of control 

 over the cells near the anterior cut surface and consequently 

 tends to prevent the development of the new head." 



Anaesthetics can interfere with these processes by inhibiting 

 the activities of the cells of the anterior cut surface, and thus 

 decreasing head frequency, and by inhibiting the increase of 

 the metabolic activity of the whole of the cut portion ; this 

 effect may overbalance the direct effect of section on the 

 anterior cells and thus increase head frequency. The ultimate 

 result depends upon the concentration of the anaesthetic, and 

 the length of period of its action. The anaesthetics employed 

 in these experiments were chloretone, chloroform, chloral 

 hydrate, ether, and ethyl alcohol. 



J. M. D. Olmsted contributes two papers dealing with 

 experimental work on Polyclads to the same number of the 

 Jr. of Expt. Zool. In " The Role of the Nervous System in 

 the Regeneration of Polyclad Turbellaria," he describes 

 experiments with Planocera californica, Phylloplana littoricola, 

 and Leptoplana saxicola which show that these species follow 

 the general rule of polyclad regeneration. They are able to 

 restore missing parts, provided the cephalic ganglia are intact, 

 but if these organs are injured, new nervous tissue is not added 

 to restore the brain to its original size, and if they are entirely 

 removed, regeneration cannot take place anteriorly, though it 

 may do so posteriorly. 



