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CEPHALOPODA. 



plane of the egg or later embryo, i.e., in the plane given in Fig. 106 

 B. This first furrow (/) above which the polar bodies are, as a rule, 

 found (Figs. 107 and 105 B, rk), starts from the middle part of the 

 germ-disc where the cleavage -nucleus lies and is continued to the 

 periphery of the disc. It cuts deepest in the centre of the disc, 

 dividing the whole of the protoplasm at this point into two segments 

 (Fig. 106 B), while, further back and especially beyond the actual 



B 



FIG. 108. Eggs of Loligo Pealii representing various stages of the cleavage of the 

 germ-disc, the bilateral symmetry of which can be recognised (after WATASE). d, 

 dorsal ; v, ventral ; vo, anterior ; h, posterior ; I, left ; r, right. 



disc where it is also prolonged (Figs. 107 and 106 A), it forms 

 merely a shallow groove in the formative protoplasm which vanishes 

 towards the equator of the egg. The same is the case with the next 

 furrows which are like the first meridional lines of cleavage (Figs. 

 107 to 109). 



The second furrow runs at right angles to the first (Fig. 107 JB, 

 II). In consequence of the furrows passing beyond the germ-disc 



