Januaby 28, 1916] 



SCIENCE 



147 



Tests made upon earthworms, clams, two genera 

 of salamanders and upon the gold fish by means 

 of carefully guarded thermoelectric measurements 

 indicate that in general these animals adjust them- 

 selves to the temperature of their environment 

 with remarkable exactitude, within a very short 

 time, the difference being usually measurable only 

 in thousandths or hundredths of a degree Celsius. 

 Observations on Segeneration and Division in 

 Ciliates: Gakt N. Calkins, Columbia Univer- 

 sity. 



A definite division zone, not affected by loss of 

 parts through cutting, has been demonstrated in 

 Paramecium and Vronychia. In Paramecium re- 

 generation of enucleated fragments never occurs, 

 while regeneration of nucleated fragments varies 

 with the race used. In Uronychia regeneration of 

 nucleated fragments always occurs, and regenera- 

 tion of enucleated fragments varies with age of 

 the cell when cut. If cut within eight hours after 

 division the latter never regenerates; if cut 

 within two hours prior to division it invariably 

 regenerates into a perfect, but enucleate, cell. 



Precocious formation of powerful cirri, before 

 division, is characteristic of Uronychia. This, and 

 regeneration, are phenomena of the same type, 

 both functions of the fully differentiated proto- 

 plasm. The experiments indicate differences in 

 protoplasmic make-up in young and old cells; and 

 the increasing power of regeneration with age in 

 enucleated fragments indicates an increasing dif- 

 ferentiation. When fully differentiated, enzymes 

 are formed leading to precocious organ formation. 

 Cell division occurs when differentiation has 

 gone a step beyond that necessary for regenera- 

 tion. Enzymes are then produced which bring 

 about cytolysis of the specialized protoplasm in 

 the division zone. Through tension of the cell the 

 membrane turns in and the cell divides by con- 

 striction. 



With chemical activities at division the proto- 

 plasm is restored to the labile undifferentiated 

 condition of young cells. If this restoration is in- 

 complete a progressive differentiation of the racial 

 protoplasm occurs, leading to depression and 

 death, which are prevented by drastic reorganiza- 

 tion phenomena of asexual, and sexual, endomixis. 

 The Distribution of Water in the Embryonic Ner- 

 vous System: 0. C. Glaser, University of Michi- 

 gan. 



Embryonic nervous systems of Sana pipiens 

 contain more water anteriorly than posteriorly. 

 Donaldson has found in the adult a difference in 

 the same sense. The determinations in the em- 



bryonic material were necessarily made with sys- 

 tems incompletely isolated from other tissues. 



An indirect method, free from this objection, 

 gives the same result. Nuclear volume varies with 

 the water content of the cell. In the nervous sys- 

 tem only relative nuclear volumes can be dealt 

 with, but the evidence from thousands of nuclei 

 shows that the anterior ones are larger than the 

 posterior, not only during folding, but also in the 

 flat neural plate. 



In the theory of autonomous folding which T 

 have tried to develop, absorption of water is a 

 symptom of surface changes in the neural cells, 

 and these changes are held responsible for the 

 folding. If correct, and if nuclear size is an index 

 of water content, then nuclei in the curling edges 

 of the neural plate should be larger than those in 

 the flat portions of the plate at the same level. 

 This, as the detailed evidence to be presented 

 shows, is true. 



From the beginning, then, the anterior end of 

 the vertebrate nervous system has a higher water 

 content than the posterior, and the absorption of 

 water accompanies folding. 



The Comparative Besistance of Marine Animals 

 from Different Depths to Adverse Conditions: 

 V. E. iShelford, University of Illinois. 

 Benthic animals from different depths differ 

 strikingly in their resistance to adverse conditions. 

 Individuals of the same species taken from differ- 

 ent depths show the same relations as do species 

 living at the same or correspondingly different 

 depths. In general animals from two fathoms are 

 two to three times as resistant to fresh water and 

 high temperature as animals from seventy-five 

 fathoms. Animals from deeper water are usually 

 more resistant to excesses of acid and alkali than 

 those from shallower. The differences in physio- 

 logical character within single species show the 

 unreliability of conclusions regarding distribu- 

 tion based on the assumption that physiological 

 characters are uniform for entire populations. 



The Change of the Blowfly Larva's Photosensitiv- 

 ity with Age (illustrated with charts) : Bradley 

 M. Patten, Western Eeserve Medical School. 

 Larvffi of the blowfly were tested each day from 

 hatching until pupation to determine what, if any, 

 changes take place in the degree of their photo- 

 sensitivity. The test employed consisted in sub- 

 jecting maggots crawling under the influence of a 

 horizontal beam of light to an instantaneous 

 change of 90° in the direction of beam. The re- 

 sulting change in the direction of the animal's 



