1904.] NATURAL SCIENCES OF PHILADELPHIA, 325 



THE CELL-LINEAGE AND EARLY LARVAL DEVELOPMENT OF FIONA 



marina, a nudibranch molltjsk.i 

 by dana brackenridge casteel, ph.d. 



Outline. 



Introduction. 



Material and Method. 



Nomenclature. 



Earlier Work on Opisthobranch Development. 



Maturation and Fertilization. 



The Unsegmented Egg. 



First Cleavage. 



Second Cleavage. 



Origin of Germ Layers. 



Segregation of the Ectoblast. 



Segregation of the Ento-Mesoblast. 



Segmentation of the Entoblast. 

 Cleavage History of the Ectomeres. 



The First Quartet. 



The Second Quartet. 



The Third Quartet. 

 Gastrulation. 



Ecto-Mesoblast 



Closure of the Blastopore. 

 Organogeny. 



The Velum. 



Later Velar Development. 



Head Vesicle. 



Nerve and Sense Organs. 

 Cerebral Ganglia. 

 Otocysts and Pedal Ganglia. 

 Eyes. 



Excretory Organs. 



The Enteron. 



Stomodaeum and Mouth. 



Shell Gland and Foot. 



Larval Musculature. 

 Change of Axis and Form of the Developing Organism . 

 Abstract. 

 Table of Cell-Lineage. 



Introduction. 



The study of the cleavage and early larval history of Fiona marina 

 (Forsk.)^ embodied in this paper was undertaken with the view of 



' Contribution from the Zoological Laboratory of the University of Penn- 

 sylvania. 



' Dr. H. A. Pilsbry, of the Academy of Natural Sciences of Philadelphia, has 

 kindlv assisted me in identification. 



