128 SUMMARY OF CURRENT RESEARCHES RELATING TO 



counteracting the influences of other substances such as bouillon. The 

 authors agree with Whitney in thinking that nutrition has some effect, 

 but further experiment is needed to test the extent of its influence. 



Echino derma. 



Effect of Radium Radiations on Rate of Cell-division in Arbacia.* 



Charles Packard finds that the eggs of this sea-urchin, exposed to a 

 brief but intense radiation during the period when the germ nuclei are 

 approaching each other, are accelerated in their rate of cell-division. 

 Less intense radiation produces less acceleration. 



Exposures made during the prophase result in an acceleration unless 

 they are prolonged, when a retardation ensues. During the metaphase 

 the same phenomena appear, but to a greater degree. During the 

 telophase the effects are much the same as in the prophase. Eggs 

 exposed during the resting stage are not easily affected. 



The power of the protoplasm and chromatin to absorb the radiations 

 does not change during the j>eriods of cell-division. The differences in 

 the density of the chromatin during the different phases of mitosis do 

 not affect its absorptive power. During the metaphase, when the eggs 

 are most responsive to radiations, oxidations take place through the 

 activity of enzymes. If these enzymes are accelerated or retarded, the 

 effect is to accelerate or retard the rate of cell-division. Experiments 

 indicate that radiations produce these effects on extracted enzymes. It 

 may be inferred, therefore, that the endo-enzymes are affected in the 

 same way, and that changes in the rate of cell-division, following radia- 

 tion, are due to the direct action of the radiations on the rate of enzyme 

 action. 



Food of Sea-urchin.t — H. N. Milligan finds that Echinus miliaris 

 eats dead or dying fishes, eggs of fishes, Ascidians, Cirripedes and small 

 Crustaceans, dead Crustaceans of larger size, cast-shells of Crustaceans, 

 freces of crabs, dead and gaping Molluscs, eggs of dog-whelks, pieces of 

 other Echinoderms, living members of the same purple-tipped species, 

 living colonies of Polyzoa, tubes of Serpulids and the like, Hydrozoa, 

 small sponges, Algse of various kinds, sand and shell-gravel — an extra- 

 ordinary range of food. 



Coelentera. 



Firth of Forth Coelentera. J — Wm. Evans records HaUclystus 

 auricula (Ratke) ; a species of Rhizostoma, probably i^. octopus (L.) ; the 

 little Medusoid Phialidium cymbaloideum (van Ben.), liberated from 

 Campamdina repens or C. turrita ; Sarsia tuhulosa, Melicertidium 

 octocostatum, Eutonina socialis, Tima lairdii, and the fine Ctenophore, 

 Bolina inftmdibulum. 



* Journ. Esper. Zool., xxi. (1916) pp. 199-211. 



t Zoologist, XX. (1916) pp. 81-99. 



: Scottish Naturalist, No. 59 (1916) pp. 283-6. 



