MEMOIRS. 



The Embryology of Clepsine.^ By Charles Otis Whitman, 



of Boston. 



Contents. 



HisTOKY : Methods — I. Okigik and Growth of the Egg. 



A. Formation of the Primitive Egg-cell, Reproductive Organs. The Egg- 



string: (1) The Rhachis; (2) The Peripheral part. 



B. Growth of the Primiiive Egg-cell to tiie Mature Egg. Eormation of the 



Yolk-spheres. Summary. 



II. Copulation, Deposit, &c. 

 Food; Time of Deposit ; Habitat; Act of Laying; Number and Colour of 

 tiie Eggs. 



III. Changes Pkeliminary to Cleavage. 



(a) Composition of the Egg : Germinal Vesicle; Reticulum, (d) Archi- 

 amphiaster: The Polar Figure ; Quiescent state; the Pellucid Spot. 

 (c) Polar Globules : Polar activity, (d) Formation of Polar Rings 

 and Pronuclei : Pronuclei, (e) Primary Cleavage-nucleus. Summary. 



Greneral Considerations. — (a) Germinal Vesicle, (l/) Pronuclei and 

 and Cleavage-nucleus. (c) Polarity; (1) Polar Rings; (2) Ring- 

 rays ; (3) " Falteukranz." (d) Polar Globules. 



IV. Cleavage. 

 («) First two Meridional Divisions ; (b) Formation of the first four Ecto- 

 blasts ; (c) Formation of the two Mesoblasts and the Primary Neuro- 

 blast ; (d) Formation of the Neuroblasts; (e) The four Ectoblasts 

 and their relation to the Month ; (/) Movements among the Cleavage- 

 products ; (ff) Relation of the Mesoblasts and Neuroblasts to the 

 Germ-bands ; (h) Formation of the Entoplasts. 



V. Gastrula and Neurula. 

 (a) Growth of the Germ-bands and the concomitant Invagination ; (i) Piia- 

 ryngeal Clefts ; {c) Nerve. chain ; (d) Segment-cells ; (<?) Segmental 

 Organs ; {/) Number of Somatomeres. 



VI. Alimentary Canal. 

 (a) The Entoderm ; (b) Origin of the Entoderm ; (c) Final position of the 

 "Residual Yolk ;" (d) Free nuclei. 



VII. Circulatory Apparatus. — Summary (Sections IV — VII.) 

 General Considerations. — («) Axial Differentiation ; {(j) Cleavage 

 Cavity; (c) Mesoderm; (d) The Gastrula; (e) The neurula of 

 Clepsiue compared with that: of Vertebrata. 



History. 

 No less than five memoirs have already been written on the 

 embryology of Cleps'me complanata, Sav. The earliest of these 



' 'Inaugural Dissertation to obtain the Degree of Doctor of Philosophy 

 submitted to the University of Leipzig.' 



VOL. XVIH. NEW SEU, P 



