LARVAE OF ARBACIA PUNCTULATA 325 



seventy-two in number while in the second they were about 

 forty-five and in the last, twenty-five. But the less numerous 

 underwent a compensating increase in diameter, so that cell size 

 was in inverse ratio to cell number. 



Godlewski ('08) confirmed the conclusions of Marcus for 

 Echinus, that ''die erhohte Temperature, die grossere Konzen- 

 tration der Salze im Seewasser, der hohere Alkalinitatsgrad des 

 Umgebenden Mediums begiinstigen die Hiiufigkeit der Zell- 

 teilungen wahrend der Furchung," so that the embryos which 

 have developed under these conditions contain a greater num- 

 ber of cells than those which have developed in lower tempera- 

 ture or in more dilute sea-water or in a lower degree of alka- 

 linity. But, since during the following period no consider- 

 able increase of absolute mass of the nuclear substance of the 

 embryo occurs, and since through the divisions of this cleavage 

 period the nuclear substance is distributed to a greater num- 

 ber of cells, it results that the nuclei of those blastulae which 

 have developed in lower temperature or in lower salt- or hydroxyl- 

 concentration, are smaller than those which have been raised 

 under the reverse condition. Consequently the absolute amount 

 of nuclear substance seems to be independent of external factors, 



Loeb ('08) determined the temperature-coefficient of the eggs 

 of Strongylocentrotus purpuratus for the time between fertih- 

 zation and the first cleavage division, and found that it varied 

 from 3.91 for the interval between 3° and 13°, to 1.74 for the 

 interval between 12° and 22°, with an average of 2.86 for each 

 ten degrees of temperature. Peter's average ('05) was 2.15. 

 Loeb's coefficient for the time from the beginning of the first to 

 the beginning of the second division, ranged from 3.33 for the 

 interval between 5° and 15°, to 1.91 for 10° to 20°, with an 

 average of 2.56. He argued that since the temperature-co- 

 efficient for the ' Lebensdauer' of the fertilized and unfertihzed 

 egg was two for each degree of temperature, ''die chemischen 

 Vorgange welche die Lebensdauer dieser Organismen bedingen, 

 nicht identisch sein konnen mit den Vorgangen, welche der 

 Entwickelung zugrunde liegen." 



JOURNAL OF MORPHOLOGY, VOL. 30, NO. 1 



