216 C. O. WHITMAN. 



—that of F. deFillippi (No. 36, 1839)— contains but little iufor- 

 mation in regard to the earlier stages. In this direction the 

 workof Ed. Grube (No. 59, 1814) is a marked improvement. The 

 two most important and most extensive memoirs are those of 

 Heinrich Ratlike, revised and i)ubhsl?ed by Professor Leuckart 

 (No. 136,1802), and Charles Robin (No. 143,1873). The most 

 recent paper is that of C. K. Hotfmann (No. 77,1877). Each of 

 these works will be duly noticed in the course of this ])aper.^ 



The method of making sections for microscopic study — not 

 in vogue at the time of Eathke^s investigations — was entirely 

 neglected by Robin, and too exclusively relied upon by HoH- 

 man. This will account for the fact that neither of these 

 authors was able to understand the germ-lamellas. 



Section-cutting has become an indispensable aid in embryolo- 

 gical researches, an aid which no embryologist can neglect with 

 impunity, but it is by no means a substitute for former methoils 

 of investigation. Section-observation and surface-observation 

 go hand in hand. 



My studies, which have been carried ou in the laboratory of 

 Professor Leuckart, began with Clepsine marginata in the spring 

 of 1876, and in 1877 were renewed and extended to three other 

 species, viz., C. comj^lajiata (sexoculata), C. biocnlata, and C. 

 heterocUta. I have made C. martjiuata the principal object of 

 study, as the eggs of this sjjecies ofl'er special advantages for 

 cutting. 



For whatever success has attended these investigations I am 

 deeply indebted to my highly esteemed teacher. Professor 

 Leuckart, whose invaluable aid, experienced counsel, and 

 cordial encouragement I shall always hold in the most grateful 

 remembrance. A complete list of the works referred to in the 

 text, by means of numbers placed above a line, below which 

 the page is given, will be found at the end of this paper. 



Mkthods. 



1. Fur fresh examination. I have used a simple nn'croscope, 

 with a magnifying power of 30 diameters. A little higher 

 power is required for observing the formation of the polar 

 globules. 



2. For sections, a. Hardened in osmic acid (-p',, ])er cent. 

 15 — 30 minutes ; weak alcohol 2 — 3 hours; strong alcohol 2 — 

 3 hours; absolute alcohol 12 — 21 hours. 



b. Stained in toto with Reale's carmine. Tiiis method has 

 given the best j)reparations for the karyolytic figures of 

 Auerbach. For later stages I have sometimes used osmic acid 



* The Arabic numerals after the word " No." and tlie numerators in the 

 fractions liirougliout tliis |)a|)er refer lo the list of authors at the cud. Tlie 

 denoniiiialors indicate the page. 



