292 SUMMAKY OF CUERENT KESEARCHES RELATING TO 



given off. Polar body formation can be induced in three ways : by 

 lowering the surface tension of the vitelline membrane so that it rises 

 from the egg : by causing the vitelline membrane to absorb water and 

 swell ; and by shaking or rupturing it. In all three cases the stiff 

 vitelline membrane is replaced by a more plastic film. Although the 

 formation of the polar body can readily be induced in any of these ways, 

 segmentation, in the great majority of cases, does not follow. As in 

 the sea-urchin egg, a gelatinization or coagulation can be demonstrated 

 to precede segmentation. In the Gumingia egg, cortical change 

 stimulates to maturation, whereas in the sea-urchin Qgg the maturation 

 process has been completed before the egg is fertilized. 



Absorption of Nutriment from Solution by Mussels.* — E. P. 

 Churchill, jun., has made a series of observations on fresh-water mussels 

 in order to test Piitter's theory that animals living in water can use, in 

 addition to " formed " food, nutriment which is in solution. He wished 

 also to test Piitter's assumption that some of such nutriment is absorbed 

 directly by the cells of the outer body-wall, especially by the gills. 



His results show that mussels can make use of some kinds of food 

 which are in solution in the water. A part, probably a small one, of 

 such nutriment can be taken up directly by the outer epithelial cells of 

 the body. 



The dissolved nutriment taken up by the alimentary canal of the 

 mussels was no doubt absorbed in the ordinary way. Numerous 

 droplets of fat were found closely attached to outer ends of the 

 epithehal cells of the gills or mantle. The absorption may be effected 

 by phagocytic or amoeboid action of the cells, or by solution in the 

 plasma membrane and re-precipitation within the cell. 



In regard to the absorption of albumin it is necessary to assume 

 either a power on the part of the cell to split the protein into its amino- 

 acids and the absorption of these as in the alimentary canal, or the 

 direct taking in by the cells of the colloidal particles of albumin by 

 means of something analogous to phagocytic action. In the case of 

 starch it seems probable also that the granules entered by amoeboid or 

 jihagocytic action. 



AVhat the author emphasizes is his proof that nutriment in dissolved 

 form can be used. It is probable that the water in which the mussels 

 normally live contains considerable quantities of solutions or colloidal 

 suspensions of protemaceous material. 



Arthropoda. 

 a. Insecta. 



Metamerism of Insect's Body.t — Charles Janet has made many 

 contributions to the question of the metameric architecture of the 

 insect's body, and he sums up his conclusions, arranging the various 

 segments in " triads " or groups of three. The first or stomenteric 



• Journ. Exper. ZooL, xii. (1916) pp. 403-24 (2 pis.). 



t Bull. Soc. Entomol. Suisse, xii. (1915) pp. 354-67 (1 pL). 



