No. 446.] 



DESMOGNATHUS FUSCA. 



121 



mognathus eggs in the corresponding stages than I have been 

 able to draw. The occurrence of the third meridional before 

 the horizontal cleavage seems also to be the rule in Acipenser 



The next stage, that of 28 cells, is shown in the sixth row, and 

 appears to consist, first, of a division of each micromere, 

 increasing their number to 16, and, secondly, of a longitudinal 

 division of the smaller macromeres A, C, E, and G, into A'. A." 

 C. C". etc., while the other four B. D. F. and H. remain 

 undivided. The subdivisions of the smaller macromeres may or 

 may not be visible from the lower pole, as is seen in the third 

 figure of the row. 



Beyond this the subdivisions cannot be followed with certainty, 

 but the last figure shown (seventh row of Fig. i) which consists 

 of 26 micromeres and 16 macromeres, 42 in all, appears in some 



respects to show some regularity, although in others it is dis- 

 appointing. We would expect, indeed, to account for the 

 increase from 12 to 16 macromeres by a subdivision of each of 

 the remaining ones, B. D. F. and H, but while this can be seen 

 to be the fact in the case of F and H, the two other new macro- 

 meres cannot well be explained by a subdivision of B and D. 

 Instead of this, they appear as those marked x and y. and the 

 relation of those and of B and D to the smaller intruded mau<.- 

 meres is such as not to allow the desired interpretation. Les> 

 difficulty appears in the interpretation of the 26 micromeres or 

 while we would naturally expect a doubling of each ot the 100 

 the former stage, and a consequent 32 in this, its smaller nunv 

 ber may well be accounted for by the supposition that some 



No definite interpretation 



16 have not yet divK 



