32 K. MITSUKURI ; 



subjects will find it easy to understand that many little difficulties, 

 however, stand in the way of realising such a course, and that the 

 labour necessary in overcoming such difficulties is not at all com- 

 mensurate with the advantages to be derived from it. Moreover, such 

 a proceeding would increase the number of figures and plates to an 

 inconvenient degree. I have, therefore, thought it best to present here 

 series of sections, selected from the three species, in such a way that 

 where the course of development is practically the same in two or all 

 of the three species, a series from one species may do office for the 

 other one or two. Series of sections are therefore given, mainly in 

 the order of their age, regardless of the species to which each may belong 

 Where there is a striking divergence between any of the three, that fact 

 will be mentioned and as far as possible illustrated Avith a series of 

 sections. The reader is for this reason requested to note specially to 

 which species each of the series given in the following pages belongs. 

 The numerals placed between every two sections give the number 

 of sections that intervene between those two. Again, when a section 

 is stated to be so many sections l^ehind another it must be under- 

 stood that that section is excluded, and that counting begins 

 from the section next to it and includes the given section behind. 

 Karyokinetic figures are filled in in some of the series, and omitted 

 from others, so that their absence in the drawing must not be 

 taken as their absence in the sections themselves. 



I confess, it is with some hesitation that I have decided to 

 present the description of the series in the shape given in the 

 following pages, for to read through a mere dry description of 

 sections, even if accompanied by figiu-es, is in my opinion one 

 of the most tiresome things, and I am afraid I may be taxing 

 unduly the patience of the reader. AVhen, however, I consider that 

 if he were present personally before me and I wished to convince 



