34 TEXT-BOOK OF EMBRYOLOGY. 



treated in the same manner. For permanent mounts the cover-glasses should be cemented. 

 The first (most cranial) piece will show the sperm in the ovum and the nucleus of the 

 latter in the resting or spireme stage. The second piece will show a distinct membrane 

 around the ovum, the sperm head, and the chromatin of the egg nucleus arranged in 

 tetrads. The third piece will show the membrane, the sperm nucleus as a fainter structure, 

 and the first maturation spindle. The fourth piece will show the membrane, the sperm 

 nucleus still fainter, the first polar body, and also the second maturation spindle. The 

 fifth piece will show the membrane, the very faint sperm nucleus, the first polar body some- 

 where around the periphery of the ovum, the second polar body, and often two chromosomes 

 remaining in the ovum. The sixth piece (near the junction of the two oviducts) will often 

 show both polar bodies and the two pronuclei (with no apparent difference between them) 

 in the resting stage. It should be borne in mind that the maturation process goes on pro- 

 gressively from the cranial to the caudal ends of the oviducts, so that it is possible to find 

 other stages between those mentioned. 



Maturation in a mammalian ovum is probably best seen in the mouse. The ovaries 

 of a mouse are fixed in Flemming's fluid, cut in either celloidin or paraffin and stained 

 with Heidenhain's haematoxylin (see Appendix). In some of the sections ova are likely to 

 be found which will show maturation spindles, or polar bodies, or some intermediate stages. 



Owing to their extreme minuteness, the study of the maturation processes in the sperm 

 cells is much more difficult than in the ova and, furthermore, since each primary spermato- 

 cyte gives rise to four spermatids and each spermatid is transformed directly into a sperma- 

 tozoon, it is necessary to consider all the generations of cells from the spermatozoa back 

 to the spermatogonia. 



Instructive specimens may be obtained by fixing small pieces of a fresh human testis in 

 Orth's fluid, cutting thin sections in celloidin and staining with haematoxylin-eosin (see 

 Appendix). 



Better results may be obtained from the testis of some small animal. Remove imme- 

 diately the testis of a recently killed mouse or rat, make an incision to insure quick penetration 

 of the fixative and fix in Flemming's fluid. Cut thin sections in paraffin and stain with 

 Heidenhain's haematoxylin (see Appendix). Different seminiferous tubules will show dif- 

 ferent stages in the development of the spermatozoa. It is scarcely possible in these prepa- 

 rations to trace the actual process of reduction of chromosomes. 



References for Further Study. 



BOVERI, T.: Zellstudien. Jena, 1887-1901. 



CHILD, C. M.: Studies on the Relation between Amitosis and Mitosis. Biolog. Bull., 

 Vol. XII, Nos. 2, 3, 4; Vol. XIII, No. 3, 1907. 



CONKLIN, E. G.: The Embryology of Crepidula. Jour, of Morphol., Vol. XIII, 1897. 



HERTWIG, R.: Eireife, Befruchtung u. Furchungsprozess. In Hertwig's Handbuch der 

 vergleichenden u. experimentellen Entwickelungslehre der Wirbeltiere. Bd. I, Teil I, 1903. 

 Also contains extensive bibliography. 



SOBOTTA, J. : Die Befruchtung und Furchung des Eies der Maus. Archiv ). mik. Anatomic, 

 Bd. XLV, 1895. 



SOBOTTA, J.: Ueber die Bildung des Corpus luteum beim Meerschweinchen. Anal. 

 Hejte, Bd. XXXII, Heft XCVI, 1906. 



VON LENHOSSEK, M.: Untersuchungen iiber Spermatogenese. Archiv. }. mik. Anatomic, 

 Bd. LI, 1898. 



WILLIAMS, J. W.: Text -book of Obstetrics. New York, 1903. 



WILSON, E. B.: The Cell in Development and Inheritance. 2d Ed., 1900. 



