No. 2, — On the Early Development of Limax.! By C. A. Koror. 
TABLE OF CONTENTS, 
Page Page 
IPOD COn eq pay ELO D. The Mesoderm . . . 75 
ILbuMetlioda» 534 37 E. Theoretical Considerations Wi 
III. Nomenclature of Spiral Clea avage 40 F. The Cleavage Cavity . . 81 
IV. General Sketeh of the Develop- EN A e el 
ONU ia de A E Oe 
Ye e v 3 PAR 3. Experimental. . . . 104 
Introduetory. . . 44| VI. Blastopore and Gastrulation . 106 
A. Orientation of the tabuo CO s. dopo asien A 
B. Discussion of Cleavage . 46|Literature Cited . . . 2 . . , 112 
C. Literature on Spiral Cleav- Explanation of Plates . . . . . 118 
BOO Lo wor 00 
I. INTRODUCTION. 
Tre question of the origin and history of the mesoderm, and its rela- 
tion to the body cavity in the Mollusca, is one of prime interest and 
importance. The employment of the mollusk as the typo of the 
* Pseudocoels? by the Hertwigs (81) in their * Coelomtheorie " was 
founded on the non-existence in mollusks of a true body cavity, the 
mesenchymatous nature of the musculature, and the origin of the ner- 
vous system, in part at least, from the mesoderm; in a word, on thé 
nature of the middle germ layer in its origin and later history. Since 
the publication of this important work many additions have been made 
to our knowledge of the Mollusca. There is a notable agreement among 
later investigators, especially Schmidt (90), Miss Henchman (91), and 
Erlanger (91), as to the ectodermal origin of the nervous system 
in this group. Studies in comparativo anatomy, particularly of that 
primitive group, the Solenogastres, have led to the general acceptance 
of the view that the pericardium of the Mollusca is the homologue 
of the colom of the “ Enterocoels" of the Hertwigs. This view is 
based upon the relationship of the pericardium to both the sexual 
and exeretory systems, embryology however having lent little support 
1 Contributions from the Zoölogical Laboratory of the Museum of Comparativo 
Zoölogy at Harvard College, under the direction of E. L, Mark, No. XLVIII. 
VOL. XXVII, — NO. 2. 3 
