454 



SCIENCE 



[N. S. Vol. XXX. No. 770 



toads, and for that reasoa we owe them every 

 protection. H. A. Allard 



Bureau op Plant Industry, 

 Washington, D. C. 



ON artificial parthenogenesis of the 



SEA-URCHIN EGG 



From July 1 until now I have been study- 

 ing artificial parthenogenesis in Arhacia punc- 

 tulata. I succeeded in rearing the larvse made 

 parthenogenetic by treatment with carbonated 

 sea-water (5 minutes) followed by hypertonic 

 sea-water (about 30 minutes) for several 

 weeks in Roscoff filter-aquaria. At the end of 

 a month there were so few alive that I did 

 not consider further attention to them worth 

 while, owing to the possibility (though im- 

 probable) of contamination with foreign plutei 

 when renewing the water (that was dipped up 

 daily at the end of the wharf at high tide). I 

 found no constant difference between par- 

 thenogenetic and fertilized larvs. 



It thus being doubtful that I could produce 

 sexually mature adults parthenogenetically, I 

 confined my further studies to early phases. 

 J. Loeb considers the essential event in artifi- 

 cial parthenogenesis to be the production of a 

 free-swimming embryo or larva — but why 

 larva rather than any other stage. In natural 

 parthenogenetic development the end result 

 may be a maturation or segmentation stage or 

 a larva or adult. Though only the reproduc- 

 tive adults are of significance to the species, 

 all are of significance to science. It might 

 also be remembered that Loeb's parthenoge- 

 netic Chwtopterus " larvse " were unicellular 

 structures, resembling trochophores only in 

 the possession of cilia and by an irregular re- 

 distribution of cytoplasm, and were incapable 

 of further development. 



In Arbacia punctulata maturation takes 

 place in the .ovary, but no segmentation oc- 

 curs without fertilization or an artificial stim- 

 ulus. The ovarian egg is surrounded by a 

 thick coat of a jelly-like proteid that swells 

 slightly and gradually dissolves in sea-water. 

 It is practically invisible, but can be located 

 by adding to the medium, Chinese ink, the 

 particles of which stick to its surface. The 

 inner surface of the jelly fits tightly against 



the egg. The jelly is stained by neutral red or 

 methylene blue, which causes it to contract 

 and i3ull away from the egg. Acids cause it to 

 contract and become more dense and sticlcy. 

 Tannin coagulates it into a coarsely granular 

 yellowish mass. Alkalies cause it to dissolve 

 more rapidly, as does also agitation. When 

 the egg is fertilized or put in " membrane- 

 forming " solutions a fluid is extruded which 

 pushes the jelly out from the surface of the egg. 

 The inner surface of the jelly is then sharply 

 defined and is probably bounded by a thin 

 membrane (the " fertilization-membrane ") as 

 spermatozoa wriggle freely through the jelly 

 but can not pass its inner surface. 



As membrane formation does not occur in 

 all parthenogenetic Arhacia eggs it was con- 

 sidered of secondary importance. The next 

 change seen in developing Arhacia eggs is the 

 migration of the red pigment plastids to the 

 surface. I first thought this due to the for- 

 mation of asters, but on sectioning could find 

 none. In the living egg these plastids take up 

 neutral red or methylene blue before other 

 parts of the egg, and in fixed material stain 

 with Delafield's hsematoxylin stronger than 

 other parts of the cytoplasm. Parthenogenetic 

 reagents when used in sufficient concentration 

 cause the pigment to diffuse out of these 

 plastids into the surrounding cytoplasm 

 and from it into the sea-water, showing that 

 both plastid membrane and cell plasma mem- 

 brane are permeable at this time. 



Loeb showed a similarity between haamolysis 

 and artificial membrane formation. It has 

 long been supposed that hssmolysis is due to 

 an increased permeability of the plasma mem- 

 brane as haemoglobin diffuses out. Ralph 

 Lillie supposes artificial parthenogenesis and 

 stimulation to be due to an increased perme- 

 ability of the plasma membrane. This as- 

 sumption is supported by my observation of 

 the diffusing out of the pigment in the 

 Arhacia egg. 



Repeating the experiments of others and 

 making new ones, I tried various types of 

 agents that cause hasmolysis or stimulation to 

 see whether they caused parthenogenetic de- 

 velopment in Arhacia. 1 succeeded in causing 

 segmentation by isotonic ISTaCl and by the 



