522 



SCIENCE. 



[N. S. Vol. XV. No. 379. 



The first phase shows a very gradual rise 

 in the percentage of development of the 

 embryo to 14 per cent, at 27°-29°, the 

 primitive streak alone showing'. The sec- 

 ond phase, beginn i ng with notochord, neural 

 plate and groove, and mesodermic somites, 

 presents an abrupt rise to 54.83 per cent, 

 of normal development at 30.75°. 



3. The normal average diameter of the 

 blastoderm of the unincubated egg, as 

 determined from the measurement of fifty- 

 nine individuals, is 4.41 mm. with a stand- 

 ard deviation of 0.4792 mm. and a coeffi- 

 cient of variability of 0.1087. 



4. The normal average diameter of the 

 area pellucida of the unincubated egg as 

 determined from the measurement of fifty 

 individuals is 2.51 mm. with a standard 

 deviation of 0.3382 mm. and a coefficient 

 of variability of 0.1347. 



5. From 136 blastoderms in which primi- 

 tive streaks have not developed, the form 

 of the area pellucida is 59 19/34 per cent, 

 round, 12^ per cent, nearly round, 23 9/17 

 per cent, oblong and 4 7/17 per cent. oval. 



6. The normal average volume of the 

 egg, as determined from the measurement 

 of 100 individuals, is 51.67 c.c, with a 

 standard deviation of 4.8602 c.c. and a 

 coefficient of variability of 0.0942. In 85 

 per cent, of fifteen unincubated eggs where 

 the volume was noted the diameter of the 

 blastoderm varies directly with the volume 

 of the egg, but the variates are so evenly 

 distributed about the average that the gen- 

 eral averages of the measurements in this 

 paper would not be especially affected by 

 this element. 



7. The introduction of successively 

 higher stages, and the increased growth of 

 blastoderms without primitive streaks as 

 the temperature rises, together with a con- 

 tinued growth of the primitive streak with 

 the non-appearance of other features of 

 the embryo at a low temperature, 20°-21° 

 to 27°-28°, would indicate a direct depend- 



ence of ontogenetic organization upon 

 warmth. 



Differentiation ivithout Cleavage in the 

 ^99 of the Annelid Chcetopterus perga- 

 mentaceus: Frank R. Lillie. 

 Iliis phenomenon was observed in both 

 fertilized and unfertilized ova. The essen- 

 tial point is briefly this : That by the action 

 of certain solutions the eggs are preserved 

 alive, sometimes for as long as thirty-six 

 to forty-eight hours, although neither cyto- 

 plasm nor nucleus divides. During this 

 period the cytoplasm slowly passes through 

 certain well-defined phases of differentia- 

 tion, the yolk accumulating in a dense mass 

 in the interior and the peripheral cyto- 

 plasm becoming vacuolated and ciliated. 

 The ciliated ectoplasm and the yolk-laden 

 endoplasm are analogous to the ectoderm 

 and endoderm of the trochophore, and the 

 phases of differentiation resemble some of 

 the normal processes; though the resulting 

 object can by no stretch of the term be 

 properly called a trochophore. 



The solutions employed were sea water 

 with the addition of KCl or CaCIj, or both 

 these salts. The eggs were left in the solu- 

 tions for an hour and then transferred to 

 sea water. If the solutions were above a 

 certain density, the formation of the polar 

 bodies was suppressed; but this did not 

 interfere with the subsequent differentia- 

 tion. During the period of time usually 

 occupied by the cleavage the eggs were 

 markedly amoeboid; in some cases (espe- 

 cially after CaCla) throwing out a bewil- 

 dering number and variety of long pseudo- 

 podia, and actually creeping like amoebae. 

 All intermediate conditions between this 

 and actual cleavage were observed. Dur- 

 ing this period, in typical cases, the nucleus 

 became enormously enlarged, and some 

 chromatin was diffused through the cell. 

 Fusion of ova frequently took place, and, 

 in solutions containing CaClj, large num- 



