PREFACE 



The sea urchin, Arbacia punctulata, which occurs along the Eastern coast 

 of North America, has for many years provided material for experi- 

 mental work on cells, done mostly at the Marine Biological Laboratory 

 at Woods Hole, Mass. The animals are readily obtained and the eggs 

 are produced in large quantities throughout the summer. This species 

 is the American Arbacia and is not found in Europe, where another 

 species, Arbacia lixula occurs. The latter species and many other genera 

 of sea urchins have been used for experimental work at Naples, on 

 the Swedish coast, in the British Isles, France, Japan, and elsewhere. 

 The eggs are fundamentally similar but differ in details. 



The Arbacia egg is an ideal cell. It is spherical, thus rendering 

 changes in size easy to determine. It is fairly simple in comparison 

 with most cells. It is quite hardy and can be subjected, without damage, 

 to moderate changes in the sea water, produced by the addition of 

 water, or salts, or anaesthetics, or other chemicals, and to changes in 

 temperature, pressure, light, and other physical factors. Harmful ef- 

 fects and recovery can be readily detected by fertilizing the egg and 

 watching its development. The granules in the egg can be moved by 

 centrifugal force, and the egg can be broken into halves and quarters 

 containing different kinds of materials in definite amounts. The ex- 

 perimental work on sea urchin eggs has included every line of approach, 

 cytology, embryology, physiology, and biochemistry, and has been 

 concerned with the solution of many fundamental problems. 



The earliest experiments on Arbacia punctulata eggs were those of 

 Jacques Loeb at Woods Hole in 1892, who wrote a paper entitled 

 "Investigations in Physiological Morphology. III. Experiments on 

 Cleavage", published in the Journal of Morphology. It dealt with divi- 

 sion of the nucleus without cleavage of the cell, caused by hypertonic 

 sea water. The next paper was that of T.H. Morgan in 1893, published 

 in the Anatomische Anzeiger, part of which was on the same subject, 

 taking exception to some of Loeb's results. 



Loeb and Morgan were succeeded by many well-known biologists. 

 We have a fine heritage of experimental research on the Arbacia egg, 

 and it is partly in an endeavor to gather together this work and make 

 it more readily available to later investigators that this book has been 

 written. 



The book is divided into four parts. The first part deals with sea 

 urchins in general — their history, which begins before Aristotle and 



