434 WESLEY R. COE, 



Structure of the Egg. 



The ripe egg of Cerehratulus marginatus measures about 0,16 mm 

 in diameter. It is provided with a nearly spherical germinal vesicle 

 which is about ^ — f the diameter of the egg, and which, instead 

 of lying exactly in the center of the cell, is usually conspicuously 

 eccentric. 



In preparations stained with haematoxylin the cytoplasm appears 

 as a reticulum made up of an ideally regular network of delicate 

 fibres , the individual microsomes of which show with the greatest 

 distinctness. In each of the meshes of the network (before the dis- 

 appearance of the germinal vesicle) lies a spherical yolk-globule. 

 These measure about 0,002 mm in diameter, although they are liable 

 to considerable variation in size. The yolk globules do not come in 

 direct contact with the cytoplasmic fibres, and this would indicate 

 either that these latter are imbedded in a more fluid matrix permeating 

 the whole cell, or that the yolk-globules have been considerably 

 shrunken by the preserving fluids. Each microsome of the network 

 stains dark blue with haematoxylin and Bordeaux red. The yolk- 

 globules stain in various ways depending on their position in the egg, 

 and on other conditions probably due to the irregular action of the 

 killing fluid. Those yolk-globules which lie near the periphery of the 

 egg are, in part, larger than those nearer the center, and are usually 

 afi'ected by the killing fluid in such a way that they hold the blue 

 stain of the haematoxylin long after it has been extracted from all 

 the others. It thus happens that in most preparations the yolk- 

 globules near the periphery are dark blue or brown , while those 

 nearer the center of the cell are red. It is possible also that there 

 may have been a difference in the original chemical composition of 

 these two classes of yolk-globules, although we find all gradations 

 between them. The blue granules of the reticulum form a very pretty 

 contrast with the red stain of the yolk globules. 



Although the cytoplasm has the appearance of a reticulum when 

 seen in sections, yet, as has often been urged, this fact forms no 

 argument against the existence of a true vesicular or alveolar structure 

 in the living egg. Indeed, the evidence all seems to point toward 

 the "alveolar theory". 



The nuclear membrane is usually, though not always, red in 

 specimens stained with haematoxylin and Bordeaux red, where the 

 reticulum of the cytoplasm is blue. This is not, however, an indication 



