4 ART. 1. T. FUJITA : ON THE FOEMATION 



bright, particularly when fresh, varying from Hght red to yeUow. 

 In advanced stages, however, the color changes completely to 

 dull brown just as in the case of Siphonaria. 



THE ELASTOMERE STAGE. 



Siphonaria : — In three or four hours after deposition, the 

 egg gradually begins to elongate in the antero-posterior dii-ection, 

 i.e. almost parallel to the long axis of the chorion. Subsequently 

 a portion becomes somewhat flattened or even depressed, and tlie 

 cytoplasm thereabout becomes translucent in the form of an 

 inverted cone. This portion begins to bulge out, and fifteen 

 minutes later it finally assumes a spherical shape. This eventually 

 separates from the mother egg, forming the first polar body. 

 After the complete detachment of this body, the egg returns to 

 its normal spherical form, and loses its transparency throughout 

 its entire mass. Then ensues an interval of about thirty minutes ; 

 after which the egg again behaves as above described. The new 

 spherical structure or the second polar body is thrown out liere 

 very close to the first. After the completion of the maturation 

 processes, the restoration of the egg to the normal spherical form 

 is again effected. Generally fifteen minutes are required for each 

 of the two processes : — the formation of the second polar body, 

 and the restoration of the spherical form. Then follows a pause 

 of one or more hours, after which the egg elongates for the third 

 time. This is the preparation for the first cleavage. If we 

 carefully observe the exact contour of the egg at this stage, 

 we shall find that it is not strictly elliptical in shape. The 

 portion which becomes the future posterior end is almost always 

 slightly pointed. Hence, using an exaggerated expression, it may 



