ARTIFICIAL PARTHENOGENESIS 473 



the Marine Biological Laboratory and the Sheffield Laboratories 

 at New Haven. My thanks are especially due to Prof. Wesley 

 R. Coe, of Yale University, whose wide acquaintance of the breed- 

 ing habits and cytology of Cerebratulus materially aided in my 

 work. I am indebted, likewise, to Prof. Jacques Loeb and his 

 associates at the Rockefeller Institute Laboratory at Woods Hole, 

 who placed at my disposal an abundant supply of sea-urchins' 

 ovaries and testes, which were not demanded in the work of 

 Professor Loeb's Laboratory. Prof. Ralph Lillie and Dr. J. F. 

 McClendon likewise contributed a supply of similar material, 

 without which I could not have obtained sufficient lecithin for 

 the work with this compound. 



The methods used in the different experiments naturally vary 

 according to the procedure, but it may be of advantage to 

 describe the principal ones which are applicable throughout. 



Fresh-water (sweet-water) was used throughout to sterilize 

 instruments and dishes from contaminating spermatozoa and 

 recourse to heat or chemical sterilization was avoided as hindering 

 the experiments in time and in danger of introducing a variable 

 wholly apart from any which might come in from natural sources. 

 The Harpswell Laboratory is so situated that the purest of sea- 

 water free from spermatozoa of Cerebratulus may be readily ob- 

 tained by taking a motor boat off shore for a mile or so at flowing 

 tide. Moreover, in this laboratory, the temperature was low 

 (on the table upon which the finger-bowls were placed, the air cur- 

 rent seldom ran above 17°C.) and it was only exceptionally nec- 

 essary to resort to ice-boxes. Hence, the normal environmental 

 factors were kept as nearly as possible throughout these experi- 

 ments. There are no large cities near the Harpswell Laboratory 

 and the conditions as far as contamination with decaying organic 

 matter which might modify results, are not to be considered. 



The worms were taken at about three-day intervals and the 

 females and males were kept isolated in battery jars beneath the 

 laboratory, where the temperature was even lower than in the 

 work rooms above. It was found necessary to isolate not only 

 males from females, but the individuals in every case from other 

 individuals, owing to the fact that the sex products were shed 



