Habits and Early Dezrlopment of Linergcs merciiriiis. 159 



fully fixed in my sections of the Lincrges egg it seems probable that the 

 layer between these two is also a normal feature of this egg. 



Furthermore, by means of high centrifugal force the substances of the egg 

 of Linergcs may be separated into three distinct zones, the lightest of which 

 is clear protoplasm, the heaviest a yellow substance crowded with yolk 

 spherules, and intermediate between these a zone of blue or blue-gray 

 material. It is difiicult to determine whether these zones correspond to the 

 three concentric layers just described, but they at least show the presence 

 of substances of different specific weights in the unsegmented egg. 



There are two kinds of spherules within the ooplasm; (i) large yolk 

 spherules ranging from 3 to 9 /^ in diameter, and (2) small spherules, 

 densely black after Flemming's fluid, which are from 0.5 to i ;«, in diameter. 

 The latter are at first distributed quite uniformly throughout the ooplasm, 

 but during mitosis they gather closely around the spindles and nuclei. 



The germinal vesicle is relatively large and contains a single large 

 nucleolus which is usually vacuolated and in some cases an additional smaller 

 nucleolus may be ]iresent (plate i, figs, i, 2). The chromatin consists of 

 small granules scattered through the achromatic ground substance (plate i, 

 fig. i). In the prophase of the first maturation this chromatin is differen- 

 tiated into oxychromatin granules and into a relatively small number of basi- 

 chromatin rods (plate i, fig. 2), which in certain stages have the form of 

 tetrads. 



Maturation and fertilization. — As maturation approaches, the germinal 

 vesicle moves up to the periphery of the egg ; in fact, the outer side of the 

 vesicle comes into contact with the cell membrane and in some cases (prob- 

 ably abnormal) the germinal vesicle is protruded from the egg as if it were 

 being squeezed out bodily (plate i, figs, i, 2). When the wall of the ger- 

 minal vesicle dissolves a relatively enormous quantity of achromatic substance 

 escapes into the cell body. 



Two polar bodies are formed in the usual manner ; iiowever. Ijotii first and 

 second maturation spindles are very small, about 0.002 part of the volume 

 of the germinal vesicle, and they exhibit neither centrosomes nor polar rays. 

 During the formation of the first polar body a lobe of clear protoplasm 

 appears at the vegetal pole, just as is the case among annelids and mollusks. 

 This lobe soon disappears and does not again reappear at the second matura- 

 tion division or the first cleavage, as it does in the cases of annelids and 

 mollusks (fig. 3). In one or two instances I have seen the head of the sper- 

 matozoon within or just central to this lobe (fig. 4), and it is possible that 

 the lobe is formed at the point of entrance of the sperm. If this be true the 

 sperm enters at or near the vegetal pole, as is the case with so many animals. 



Hargitt (1906) believes that in Clara, Pennaria, and Eudendriuin no 

 mitotic figures are present during maturation and " that the reduction 

 phenomena of maturation may well be accomplished without any of the 



