THE DIVIDING SEA-URCHIN EGG 
289 
chemical composition and structural density, such as determine 
the semi-permeability of a precipitation-membrane, but is insep- 
arable from the living condition, i.e., is actively maintained by a 
continual process of metabolism. The proof of this is that death — 
the cessation of metabolism — however caused, is invariably fol- 
lowed by a loss of semi-permeability, i.e., the normal state of the 
membrane then ceases to be maintained and the unhindered 
processes of diffusion lead to the disintegration of the cell. 
Hence destruction of the surface-layer by artificial means - 
cytolytic substances, heat, extensive mechanical injury — is quick- 
ly fatal to all cells. 
In the experiments about to be described, I have studied the 
behavior of fertilized Arbacia eggs when subjected for definite 
brief lengths of time to various concentration of some of the 
higher alcohols — anyl, hexyl, heptyl, octyl and capryl — at dif- 
ferent periods of the cell-division cycle. This work was under- 
taken at the Marine Biological Laboratory, at Woods Hole, 
Massachusetts, during the past summer (1919) at the suggestion 
of Professor Ralph Lillie, to whom the writer expresses his hearty 
thanks for many kind suggestions and directions during its prose- 
cution. 
EXPERIMENTATION 
In order to procure a sufficient number of eggs for each series 
of experiments, between one and two dozen large females were 
opened, and their eggs collected into finger bowls. By successive 
washing and settling, a uniform mass of mature eggs was obtained, 
which could be inseminated and divided into two parts ; one to be 
used for the control, and the other for the experiments. It was 
found early in the work that the success of the experiments de- 
pended upon having batches of eggs which were sufficiently 
mature and uniform, so that all eggs reached successive stages 
in their development at practically the same time. It was also 
found that great exactness in the time-relations of the operations 
was absolutely essential, and that any variation once entered upon 
was sufficient to make the results worthless from a comparative 
standpoint. Usually two series of experiments were started in 
a day ; one in the morning to be carried over to the gastrula stage 
by the following morning, and one in the afternoon, to be ex- 
amined the following afternoon. After extended preliminary 
experimentation, it was found convenient, in any one series, to 
keep the time of exposure constant and to vary the concentration 
of substance used, although in a considerable number of experi- 
