148 



SCIENCE 



[N. S. Vol. XLIII. No. 1100 



locomotion was measured in degrees by means of 

 a protractor. The more sensitive the individual 

 was, the more closely did its deflection approach 

 90°. Using the same larvas throughout the experi- 

 ments, one hundred trails were run each day. The 

 average deflection of each of these sets of 100 

 trails was used to locate a point on an "age- 

 sensitiveness" curve. 



The curve of photosensitivity thus obtained 

 shows a rapid rise during the first days of larval 

 life, reaching a maximum on the fourth day with a 

 deflection of 81°, and gradually dropping off till 

 the time of pupation, when the average deflection 

 was 58°. 

 The Physiology of Chemoreceptors : W. J. Ceoziee, 



Bermuda Biological Station. 



A comparison of quantitative measurements of 

 cell penetrability for acids with the relative stim- 

 ulating powers of these acids and with the limit- 

 ing dilutions beyond which they are ineffective in 

 stimulating earthworms and four species of ma- 

 rine animals indicates: (1) that an acid stimu- 

 lates by union with a constituent of the ceptor 

 surface, and (2) that this surface is not simple 

 but complex and contains probably proteins and 

 fatty substances. 



Enoystment of Didinium nasutum: Gabt N. Cal- 

 kins, Columbia University. 



Encystment of Didinium under culture, with 

 adequate food and normal conditions, is preceded 

 by a declining division rate in the race as a whole. 

 Encystment lasts for about six days, when the or- 

 ganisms emerge with renewed vitality, as shown by 

 an average division rate from five to ten times 

 greater than that prior to encystment. 



During encystment the cell undergoes complete 

 reorganization. The macronucleus degenerates into 

 fragments which are ultimately absorbed in the 

 protoplasm. The micronuelei swell and divide by 

 mitosis, the products giving rise to new macro- 

 and micro-nuclei. 



This reorganization occurred twice during the 

 history of my Bidinium culture with an interval 

 of six weeks. After the second period the race did 

 not encyst again, but continued to live with a 

 slowly decreasing division rate for about six 

 months, when the last individuals died with char- 

 acteristic symptoms of depression. 



The individual Bidinium isolated was evidently 

 well advanced in its racial cycle. This is indi- 

 cated not only by loss of powers of encystment and 

 reorganization, but also by the fact that after the 

 two periods of encystment, and for ten days only 



in each case, epidemics of conjugation occurred in 

 the stock material derived from organisms which 

 had recently encysted. Asexual reorganization, ap- 

 parently, merely restored the protoplasm to a con- 

 dition in which conjugation was possible; a con- 

 dition which is, in itself, evidence of advanced 

 differentiation, and a condition from which the 

 protoplasm is restored through conjugation. 



On Cell Penetration hy Acids: The Effects of 

 Anesthetics and of Stimulation hy Induction 

 ShocJcs: W. J. Ceoziek, Bermuda Biological Sta- 

 tion. 



1. Anesthetics produce a reversible decrease in 

 the permeability of Chromodoris tissues toward a 

 range of dilutions of strong acids. The magni- 

 tude of the effect depends upon the concentration 

 of the individual anesthetic and the time of its ac- 

 tion, and may prolong penetration time by 100- 

 200 per cent. Following the decreased permea- 

 bility there ensues an increased permeability, irre- 

 versible in its later stages, which can be antagon- 

 ized (delayed) by balanced salt solutions. Cyto- 

 lytic agents increase permeability toward acids. 



2. Stimulation by induction shocks decreases 

 the penetration time of acids. The decrease in 

 permeability toward acids produced by anesthetics 

 may be inhibited by simultaneous strong stimula- 

 tion. 



Behavior of Holothuria captiva Toward Balanced 

 Illumination: W. J. Ceoziee, Bermuda Biolog- 

 ical Station. 



The whole surface of Holothuria is reactive to 

 light. These animals are negatively phototropic. 

 In H. captiva the two sides of the animal are 

 sensibly parallel, and when subjected to bilateral 

 illiunination there is accordingly no possibility of 

 equalizing the amount of light on the two sides by 

 assuming a position perpendicular to the axis of 

 the opposed beams, or, in case these beams are of 

 unequal strength, by pursuing a path at some 

 definite angle with this perpendicular. This is in 

 accord with the behavior of Holothuria and proves 

 that photic stimulation in this animal depends 

 upon the amount of light falling upon the sensi- 

 tive surface, and is independent of the angle of 

 incidence. The fact that isolated portions of the 

 skin react to continuous light is further and con- 

 clusive evidence that the direct action of light, not 

 change of intensity, furnishes the stimulating 

 agency. 



Caswell Grave, 

 Secretary-Treasurer 

 (To lie continued) 



