1904.] 



NATURAL SCIENCES OF PHILADELPHIA. 



353 



The table should be read : In A quadrant 2a^^^ cleaves first, 2a2" second, 

 2a"^ third and 2a^^^ fourth. In B quadrant, etc. Cleavages in A 

 quadrant are found in figs. 50, 58 and 63; in B, figs. 52 and 59; in C, 

 figs. 44, 48, 54, 60 and 65; in D, figs. 47, 51 and 61. 



The divisions of 2a^^^-2d^^^ are Iseotropic in all quadrants, of 2a^"-2d^" 

 universally dexiotropic, of 2a^^^-2d^^ everywhere dexiotropic, while 

 variation is found in the direction of cleavage in the cells 2a^^^-2d"2. 

 Of these latter a decidedly Iseotropic direction is found in B quadrant, 

 horizontal to dexiotropic in D, horizontal to Iseotropic in A and ap- 

 proximately horizontal in C. With regard to the size of the derivative 

 cells, it may be said in a general way that variation is evident. More 

 particularly considered the following conditions are found to prevail. 

 The divisions of 2a^^^, 2c^^, 2d^^ result in cells of equal size, while in 

 the case of 2b^^ the upper cell 2b^^" is much smaller than 2b^^^ ; 2a^", 

 2b^", 2d^" form upper small and lower larger parts, while 2c^" divides 

 equally; 2)0^^, 2c^^^, and 2d^^^ show similar divisions into upper small 

 and lower large cells, while 2a^^^ remains so long undivided that its 

 derivatives are uncertain ; 2a^^^-2d^^^ divide equally. 



As a result of the foregoing cleavages the second quartet contains 

 in all approximately forty cells. The irregularities which have char- 

 acterized the preceding divisions are increased in number as cleavage 

 continues, though until a much later period all four quadrants show 

 relatively the same number of cells for this quartet. If figs. 67-70, 

 representing the different sides of the same egg, be examined it will 

 be seen that in A quadrant 2a^^^ has divided dexiotropically, while 

 2a^"^ has divided horizontally; quadrant B shows no further multi- 

 pHcation of elements ; in C quadrant, 2c^^^^ is in process of division, while 

 2c^"^ and 2c^"^ have both given off small cells toward the upper pole; 

 D quadrant remains as before. 

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