336 



GERMINAL ORGANIZATION 



INDUCTION PHENOMENA 



the first maturation spindle (Fig. 24, left) and may increase in number if unfertilized 

 eggs linger at maturation stages. In sea-urchin eggs stained just after their fertilization, 

 the secondary granules appear at the streak stage. If eggs are stained at later stages, 

 only a-granules will be seen during the mitotic cycle concerned, but as soon as a new 

 cleavage has taken place, the P-granules will be observed (Fig. 25). Their number 

 increases during the three or four first steps of cleavage (Fig. 23) ; then, a gradual 

 fading excludes further appreciation. In clam and oyster eggs, [i-granules are seen to move 



fi 



Fig. 28. (a) Section of a pressurised centrifuged Arbacia p. egg at the pronuclei stage. Alcian 



blue technique after picric-formalin fixation showing a selective staining of the [i-granules 



sedimented in the lower hyaline band. 



(b) same technique, but applied after oxidation by sulfuric permanganate. In addition 

 to the [i-granules, Alcian blue now stains the a-material, concentrated in the upper-vitelline 

 band, part of it being still mixed with the yolk. In a and b, centripetal side up (with lipid 

 droplets on top), centrifugal side down (with yolk and pigment). From Mulnard, Auclair 



and Marsland, 1959. 



(c) a section of a Chaetopterus p. egg at metaphase of first mitotic cleavage, fixed by picric 

 formalin and stained by Alcian blue. Selective staining of [i-granules scattered in one of 



the astral zones. 



(d) an egg of Chaetopterus p. centrifuged at the pronuclei stage, mounted in toto after formol 

 saline fixation and revealing acid phosphatase. Positivity of the yolk mass and of the 

 a-granules (below, mainly due to a-material) and of the [^-granules and diflfused material 

 (x) around the pronuclei (n = one nucleolus) in the upper hyaline zone. From Mulnard, 



1958. 



