September 26, 1913] 



SCIENCE 



447 



are cytolized, and in three minutes this is 

 true of most of the eggs. 



The membrane in question is a true fer- 

 tilization membrane, and if at the proper 

 moment the eggs are brought back into nor- 

 mal sea water, or better still, hypertonic sea 

 ■water (50 c.c. sea water + 8 c.c. 2.5 N NaCl), 

 cleavage takes place. Since July 18 I have 

 succeeded in rearing a considerable number 

 of ciliated laryse. 



II. THE INITIATION OP DEVELOPMENT WITH EGG 



EXTRACT 



If fresh ovaries of Arhacia are ground up 

 in a mortar with pulverized glass and a small 

 quantity of sea water, the liquid, when fil- 

 tered, has a color not unlike that of blood 

 serum. This fluid, if allowed to act on ripe 

 eggs contained in an equal quantity of sea 

 water, proves to be an excellent initiatory 

 agent, for if the eggs after one to two hours 

 are placed in normal sea water, many divide, 

 although no fertilization membrane appears. 



III. THE THEORY OF INITIATION, PARTHENOGEN- 

 ETIO METHODS AND THE FERTILIZATION 



MEMBRANE 



It is well known that development can be 

 induced in many kinds of eggs by very di- 

 verse means — lipoid solvents, increased os- 

 motic pressure of the surrounding medium, 

 ■electricity, heat, cold, mechanical shock and 

 even pricking the egg surface, have all proved 

 •effective in one case or another, but so far as 

 I am aware the use of egg extract from the 

 «ame species is new, as well as the production 

 of genuine fertilization membranes in Arbacia 

 punctulata by means of dilute sea water. In 

 one of the California sea urchins, Loeb^ has 

 reported the formation of membranes after 

 "the addition of distilled water, but from cer- 

 tain details it seems that the fertilization 

 membrane of at least one of the California 

 urchins resembles that of Asterias forhesii, 

 :and this differs quite markedly from that of 

 Arhacia punctulata. 



Loeb,^ on the basis of his own investigations 



'lioeb, Jacques, "Die chemische Entwicklungs- 

 ^rregung, etc.," Julius Springer, Berlin, 1909. 



and those of others, has formulated a theory 

 on the initiation of development which for 

 normal fertilization and certain of the par- 

 thenogenetic methods, postulates (a) an in- 

 creased permeability of the ovum due to the 

 action of lipoid solvents or hsemolytic agents; 

 (b) the formation of a fertilization mem- 

 brane in consequence of this superficial cy- 

 tolysis. 



Of an increase in permeability synchronous 

 with the initiation of development there is 

 not the slightest doubt, although the great 

 variety of parthenogenetic methods long ago 

 indicated that permeability is increased, in 

 other ways than by action on surface lipoids. 

 With the employment of some parthenogenetic 

 methods, fertilization membranes appear, with 

 others, not, and even the employment of lipoid 

 solvents themselves may or may not be fol- 

 lowed by the appearance of a fertilization 

 membrane. One and the same egg, as in the 

 present case, may be induced to develop with 

 or without the appearance of such a mem- 

 brane. 



rv. EXPERIMENTAL ANALYSIS OF THE FERTILIZA- 

 TION MEMBRANE 



According to Kite's^ dissection, the egg of 

 Arhacia has a vitelline membrane tightly 

 glued to its surface. Outside this is a thin 

 jelly. The appearance of the fertilization 

 membrane, according to this description, is 

 due to the swelling of the vitelline membrane, 

 and the formation of a phase boundary be- 

 tween it and the thin outer jelly. 



This description I believe to be essentially 

 correct for the following reasons : 



1. The fertilization membrane also has an 

 inner visible boundary. In certain localities 

 of the two- and four-cell stage this inner sur- 

 face of the fertilization membrane is plainly 

 visible, has indeed been often figured and I 

 believe misinterpreted. In the stages in ques- 

 tion a narrow perivitelline space can be seen 

 around the egg, but the fertilization mem- 

 brane adheres to the egg surface here and 

 there by strands. As a consequence, when 



' Kite, G. L., ' ' The Nature of the Fertilization 

 Membrane, etc.," Science, Vol. XXXVI. 



