408 RECORD OF CURRENT RESEARCHES RELATING TO 



tilaginous cell differs in different regions ; thus, in the cranial plates 

 of the tadpole the nuclei are homogeneous, and composed of solid 

 elements of delicate structure ; in most of the cartilages of the adult 

 frog or triton the solid elements of the nucleus are more thick and 

 coarse ; but between these two there arc various intermediate stages. 

 This nucleus may undergo movements, as a whole, and these are in- 

 dependent of the position which it occupies in the cell ; but when it 

 is situated in the eentre of the protoplasmic mass it moves irregularly, 

 while when it is found at the periphery it passes from right to left, or 

 vice versa. These movements are due to the solid elements of the 

 protoplasm around the nucleus, and are solely due to them. The 

 solid elements within the nucleus are no less contractile than those of 

 the protoplasm ; that they are rarely seen is due to the circumscribed 

 space in which they are found. The intensity of the movements may 

 be increased by raising the surrounding temperature to 20°-25° C. ; 

 each element of the nucleus may then be seen to be executing free 

 and independent movements, and the nuclear liquid is stirred into 

 activity. 



From these observations the author draws the conclusion that it is 

 incorrect to give the name of " reticular structure " to the refractive 

 elements of the nucleus ; for just as the protoplasm of the cartila- 

 ginous cell is composed of two different substances, one almost homo- 

 geneous and liquid, the other of contractile and freely moving ele- 

 ments, so too is the nucleus ; and the capsule on the one side and 

 the nuclear membrane on the other form a boundary for the consti- 

 tuents of the coll and of the nucleus respectively. 



Growth as a Function of Cells.* — Mr. Minot is of opinion that 

 the weight of an animal depends on the number and size of its cells, 

 and that these two variables require to be determined before we can 

 speak definitely as to the phenomena of growth. He points out that 

 the growth of a body is usually measured by its weight, but that this 

 method takes no account of the amount of non-protojilasmic matters 

 present. All Metazoa, at any rate, pass through successive cycles, in 

 which we can distinguish the two processes of senescence and of 

 rejuvenation ; substituting for Huxley's term individual, or Haeckel's 

 name person, the expression hiad, we see that in one cycle of cells 

 the number of biads varies, for Hydroids, Cestoids, Naids, &c., have 

 several, whereas the higher animals have only one. As growth is a 

 function of rejuvenescence effected by impregnation, it follows that 

 growth can only be measured by taking into account the number of 

 cells living at any given time, whether they form one or several 

 biads. 



The impregnated egg gives rise to successive generations of cells, 

 and as the parent generation disappears when division takes place, 

 two generations of cells can only exist at once when they are of 

 different lineage, but as cells do not all develop simultaneously the 

 cells of the body only belong to one generation upon the average. 

 From this conception the author establishes the following laws : — 



* 'Proc. Boston Soc. Nat. Hist.,' xx. (1879) p. 190. 



