lOO ANDREWS. 



Starfish and echinus eggs, first observed by me in 1893 at 

 Wood's Holl, when they formed one of the strongest incentives 

 to these researches. 



Butschli ascribes aster appearances in segmenting eggs to 

 an optical effect of linearly placed and stretched alveoli, and 

 to illustrate this, has figured a cross section of a preserved 

 sea-urchin egg, showing in the "attraction sphere" an indu- 

 bitable radial and linear arrangement of the vesicles. While 

 an optical striation is undoubtedly produced by the condition 

 shown, I am unable to identify this with the appearances of 

 the living tgg ; and it is surely impossible to explain thus 

 other phenomena seen there. In the " attraction sphere " as 

 figured, radial increment of substance is compensated for by 

 increase of size in the alveoli whose walls form the striae ; in 

 the living tgg, where the outer cytoplasmic foam diminishes 

 the size of its vesicles towards its periphery, such a condition 

 ceases to be possible ; moreover the rays do not appear in 

 divergent pairs after leaving the "attraction spheres," as, if 

 they were due to lines of alveoli, the conditions of increasing 

 number and decreasing size of the vesicles with increasing 

 diameter of the &gg mass would seem physically to require. 



In the living egg the aster rays follow at times very waved, 

 or truly curved, courses which are not simply complexes of 

 lines formed by alveolar walls, but are irregular with respect 

 to even single walls. The rays wander about also in a variety 

 of ways as referred to above, often progressing more as filose 

 formations than as waves of contraction influence, yet at other 

 times gaining, or losing, emphasis in a truly contractile man- 

 ner. They have no fixed course ; they curve more or less from 

 moment to moment ; they extend themselves now here, now 

 there, or conversely shorten ; they even ramify and anastomose 

 like true filose formations ; yet, during such changes the sur- 

 rounding, or even bordering alveoli, may show no change of 

 contour and even no change of place. 



At one point in their history they extend far beyond the 

 median line of an as yet undivided cell mass, passing between 

 the rays proceeding from the opposite aster, and being in- 

 terlaced changefully amongst these. After an innumerable 



