QUARTERLY CHRONICLE OF MICROSCOPICAL SCIENCE. 199 
the primordial cranium, so that a portion of external 
skeleton becomes internal skeleton. The bones thus derived 
are the secondary or investing bones of the primordial cra- 
nium or the membrane bones. 
The remaining bones of the cranium, the so-called primary 
or cartilage bones are ossified portions of the primordial 
cranium. In the amniotic vertebrates only small portions 
of the primordial cranium remain, partly because of ossifi- 
cation, partly because the investing bones cause the absorp- 
tion of and replace those portions of the primordial cranium 
which they cover. 
XII. Sexual Organs.—1l. Development of Spermatozoa.— 
La Valette St. George (‘ Arch. f. Mikr. Anat.,’ vol. x, p. 
495, plate xxxv) continues his researches on the subject, 
treating specially of certain arthropoda and mollusca, refer- 
ring also to the observations of Balbiani, Metschnikow and 
Biitschli. 
2. Changes of the Graafian Follicles. — Slaviansky 
(‘Archives de Physiologie,’ Nos. 2 and 3, 1875) gives the 
result of some elaborate researches on the development and 
maturation of the Graafian follicles, which he believes to 
be quite independent of menstruation. 
3. Accessory Glands of the Sexual Organs.—Langerhans 
(¢ Virchow’s Archiv,’ lxi, p. 208) discusses the histology of 
the prostate, vasa deferentia, and vesicule seminales. 
