before their students a series of illustrations whose fidelity is beyond question, and which 

 may serve as a basis for either elementary or advanced work in this direction. 



Following is a partial list of the points clearly shown in the present series : The 

 ovarian egg, with germinal vesicle, germinal spot and chromatin-network ; the polar 

 amphiaster with the " Vierergruppen " or quadruple chromosome-groups; the unfertilized 

 egg, after extrusion of the polar bodies ; entrance of the spermatozoon, the entrance-cone ; 

 rotation of the sperm-head, origin of the sperm-aster from the middle-piece, growth of the 

 astral rays; conjugation of the germ-nuclei, extension and division of the sperm-aster; 

 formation of the cleavage-nucleus ; the attraction-spheres in the resting-cell ; formation of 

 the cleavage-amphiaster, origin of the spindle-fibres and chromosomes ; division of the 

 chromosomes, separation of the daughter-chromosomes; structure and growth of the 

 astrosphere ; degeneration of the spindle ; formation of the " Zwischenkorper " ; origin of 

 the chromatic vesicles from the chromosomes ; reconstruction of the daughter-nuclei ; 

 cleavage of the ovum ; the two-celled stage at several periods showing division of the 

 archoplasm-mass, " attraction-spheres " in the resting-cell, formation of the second cleavage- 

 amphiasters. 



FROM THE PRESS 



"A work which is an honor to American scholarship." Philadelphia Evening Tele- 

 graph. 



" Professor Wilson has rendered a great service to teachers and students in the publica- 

 tion of the splendid series of micro-photographs of these different processes. These are 

 accompanied by an admirably lucid text." The Dial. 



" It is not often that one is permitted to examine a piece of work which is done, in all 

 respects, on an ideal standard, as this is. ... It is safe to say that the whole area engaged 

 in the fertilization and division of the ovum has never been shown or the forces traced 

 with such precision before." The Independent. 



" Every biologist owes the greatest gratitude to the authors and publishers of this 

 beautiful volume; and only those who have labored themselves to make good photo- 

 graphic plates from specimens exhibiting karyokinesis, can appreciate the wonderful 

 delicacy of the results." Natural Science. 



" This work is of a very high order, and both by its merit and its opportuneness is a 

 noteworthy contribution to science. . . . The pictures obtained represent the highest 

 perfection of micro-photography yet reached, especially as applied to protoplasmic struct- 

 ures. ... To the whole is prefixed an abundantly illustrated "General Introduction" 

 in which Professor Wilson gives a summary of our present knowledge of our history of 

 the ovum, so far as it has any bearing on the problems of fertilization. It would be very 

 difficult to surpass this introduction, owing to its felicitous combination of terseness, 

 clearness, and completeness. The work takes its place at once as a classic, and is certainly 

 one of the most notable productions of pure science which have appeared in America. 

 It will be valuable to every biologist, be he botanist or zoologist, be he investigator or 

 teacher." Science. 



THE MACMILLAN COMPANY, 



66 FIFTH AVENUE, NEW YORK. 



