540 SUMMAEY OP CURRENT RESEARCHES RELATING TO 



present in large numbers in tlie fluid yolk ; the nucleus of the endo- 

 blast-cells is most remarkable for the changes which it undergoes in 

 position. The author was most struck by the cells which appeared 

 to open superiorly, and took them at first for artificial products; 

 observation, however, led him to conclude that this was a definite 

 physiological stage, and that being so he is compelled to suppose that 

 the endoblast-cells do not merely maintain existence by diifusion, but 

 also by direct massive wandering ; there would appear to be not only 

 a completely mechanical intaking, but as complete an outgiving of 

 yolk-spheres. 



The author has also made some observations on the chick, and 

 the result of his studies is his conviction that the cells of the 

 endoblast take up food in an amoeboid manner. He finds that ecto- 

 blastic cells have a similar power of incorporating yolk-material, 

 which they do by means of amoeboid movement. In Lacerta agilis 

 he has observed protoplasmic processes directed towards the vitel- 

 line membrane, and has found in the interior of the cells small 

 yolk-granules, and others which seemed to have been just incor- 

 porated. 



In the acroblasts — as Kollmann terms the cells in the layer which 

 lies between the ectoblast and endoblast — each of which is quite 

 independent of the mesoblast, and in the cells derived therefrom 

 which he calls " poreuten," a similar phenomenon has been observed. 

 The latter are quite easy to find in the lizard, but are more difficult 

 of detection in the chick, where they can only be seen after staining. 

 In the lizard the author has been able to observe a direct movement 

 of masses from the endoblast to the poreutes, a poreute sending out 

 processes towards an endoblast-cell. 



The author concludes with referring the reader especially to the 

 work of Metschnikoff, in connection with which he would wish his own 

 fragmentary contribution to be studied. 



Larval Theory of the Origin of Cellular Tissue.* — A. Hyatt 

 reviews the history of investigation among sponges ; concluding that, 

 though true Metazoa, they possess characteristics which show them 

 to be derived from Protozoa. The parallel between the development 

 of the cell and egg in the tissue is strictly parallel with the evolution 

 of nucleated from unnucleated forms in Protozoa. Recent investiga- 

 tions have removed all objections to the homology of the egg or any 

 cell with the adult of the nucleated protozoon ; and the principal 

 mode of reproduction by division is the same in all these forms. The 

 egg builds up tissue by division after being fertilized by the male or 

 spermatozoon, just as the spermatozoon builds up colonies after ferti- 

 lization. 



Spontaneous division of a cell which undergoes encystment takes 

 place and the spermatozoa which result from this are true larval 

 monads. These resemble the monads derived from division of the 

 encysted bodies of Protozoa in their forms and in their activity. 

 They differ in being able to fertilize the female or ovum at once, 



* ScicMe, iii. (188i) p. 337. 



