VIII. On the Development of Oecanthus niveus and its Parasite, Teleas. 1 



By Howard Avers. 



First Walker Prize Essay of the Society for 1883. 



CONTENTS. 



I. Introduction— Alphabetic list of the litera- g. Formation of stomodaeum and procto- 



ture. daeum. 



II. Reproductive organs of the female. — Origin h. Revolution. 



and Maturation of the Ovum. i. Yolk sac. 



a. Ovariole. j. Synopsis of subsequent development. See 



b. Germarium. Germ cells. P- 246. 



c. Vitellarium. Follicular epithelium. k. Cells, nuclei and nuclear phenomena. 



d. Yolk. IV. Theoretical Considerations. 



e. Membranes. a. Embryonic membranes. 



f. Mature egg. Germinative vesicle. b. Yolk sac. 

 III. Origin and 'Growth of the Embryo. c. Dorsal organ. 



a. Cell elements of the fecundated egg. d. Gastrulation and neurulation. 



b. Embryo. V. Parasites. _ 



c. Primitive segmentation. a. Fungi, etc. 



d. Embryonic membranes. b. Teleas. 



e. Appearance of appendages. VI. Explanation of the plates. 



f. Neurulation. 



In this thesis I have endeavored to establish, among others, the following points. 



FOR OECANTHUS. 



1. The origin of the ovum in a germarium rather than from an ovarian epithelium. 



2. The process of yolk formation by cell degeneration instead of secretion. 



3. The occurrence of a primitive segmentation of the embryo before the appearance of 

 the permanent segments. 



4. The existence of a pair of appendages (some of them rudimentary) on each of the 

 seventeen segments of the body. 



5. The origin of the dorsal vessel as a paired organ, the lateral halves of which fuse arid 

 give rise to a median tube in the same manner as in some of the worms, and the origin of 

 the blood corpuscles as nucleoli of endodermic cells. 



6. The existence of embryonic gills. 



7. The lack of any sharp distinction between a cell and its nucleus, and between a 

 nucleus and its nucleolus. 



8. The existence of segmental enlargements of the mesodermic somites, similar to those 

 from which the nephridia of worms take their origin. 



9. The origin and significance of the embryonic membranes among the Insecta. 



10. The origin and significance of the dorsal organ among the Insecta. 



FOR TELEAS. 



11. The absence of embryonic membranes. 



12. The occurrence of a larval form intermediate between the blastosphere and the 

 cyclops larva of Ganin. 



1 The following investigations were carried on under Comparative Zoology, at Harvard College, Cambridge, 

 the direction of Dr. E. L. Mark, at the Museum of Mass. 



MEMOIRS BOST. SOC. NAT. HIST. VOL. III. * 29 



