1896. | NEW YORK ACADEMY OF SCIENCES. 175 
correspondence is almost complete. Moreover, during midana- 
phase these investigators obtain two small amphiasters at the 
poles of the first cleavage figure in all respects similar to those 
of my fig. 16. In Physa, however, there is no large centro- 
sphere, and consequently no previous peripheral wandering of 
the centrosomes.—June, 1896. | 
LITERATURE REFERRED To. 
1. BOVERI. ZELLEN STUDIEN III. 
2. FS Ueber der Verhalten der Centrosomen bei der Be- 
fruchtung des Seeigel eies. Wurzburg. 1895. 
3. DRUNER. Studien ber den Mechanismus der Zelteilung. Jen- 
aische Zeitschr. f. Naturwiss. Bd. 29. N. F. 22. 
1894. 
4. HACKER. Ueber den Heutigen Stand der Centrosomfrage. Ver- 
handlungen der deutschen zool. Gesellschaft. 1894. 
5. HILL. Notes on the Fecundation of the eggs of Sphzerechinus 
granularis and on the Maturation and Fertilization 
of Phallusia mammillata. Quart. Journ. Mie. Sci. 
1895. 
6. KORSCHELT. Ueber Kernteilung, Eireifung und Befruchtung bei 
Ophryotrocha. Zeitschr. F. wiss. Zool. Bd. LX. 
1895. 
7. MEAD. Some Observations on Maturation and Fecundation in 
Cheetopterus pergamentaceus. Cuv. Journ. of 
Morph., Vol. X. 1895. 
8. Vv. RATH. Ueber den Feineren Ban der Drtisenzellen des Kopfes 
von Anilocera mediterranea Leach, in speciellen, 
und die Amitosenfrage in Allgemeinen. Zeitschr. 
F. wiss. Zool. 1895. 
9. REINKE. Untersuchungen tiber Befruchtung und Furchung des 
Eies der Echinodermen. Sitzungsber. d. Atad. d. 
Wissench., Berlin, 1895. 
10. WILSON AND MATTHEWS. 
Maturation, Fertilization and Polarity in the Echino- 
derm Egg. Journ. of Morph., XV., Nr. 1. 1895. 
11. WILSON. Archoplasm, Centrosome and Chromatin in the Sea 
Urchin Egg. Journ. of Morph., Vol. XI. 1895. 
12. WILSON. Atlas of Cytology. 
EXPLANATION OF PLATES. 
Figs 1, 2, 4, 5, 8, 9, 10, 11, 12, 17 and 18 were drawn by Prof. Wilsonand 
the writer ; the remainder were drawn by the writer. 
PLATE IX. 
Fic. 1. The egg ten minutes after fertilization, showing the minute asters 
and their focal centrosomes, also the large black nucleolus. 
Fic. 2. Somewhat later stage several tetrad groups have been already 
formed. 
