CONTENTS. 



III. Morphology of the Gonosome .... 



1. General View of the Gonosome 



2. The Adelocodonic Gonophore (Sporosac) 



3. The Phanerocodonic Gonopliore (Gonocheme, Sexual Medusa) 



4. The Blastostyle ..... 



5. The Blastochcme (non-Sexual Medusa) 



6. Honiological Parallelism between Sporosac and Medusa 



7. Honiological Parallelism between Hydranth and Medusa 



8. Further Modifications of the Gonosome 



9. The Generative Elements .... 



Ova ..... 



Spermatozoa ..... 



IV. Development 



1. Development of the Bud. — Zooidal Development . . .67 



a. Development of the Hydranth . . . .68 



Hydrantb-bud in the Gymnoblastca and Eleutheroblastea . 68 



Spontaneous Decapitation and Re-formation of successive 



Hydranths . . . . .69 



Polarity of the Hydroid . . . .70 



Hydranth-bud in the Calyptoblastea . . .71 



b. Development of the Blastostyle . . . .73 



c. Development of the Sporosac . . . .74 



d. Development of the Medusa . . 76 



Formation of Buds by the Medusa . . .82 



2. Development of the Ovum. — Embryonal Development . . 85 



Development of the Embryo from the commencement of the Segmen- 

 tation of the Vitellus to the attainment of the Free Locomotive 

 Stage . . . . . .85 



Further Development of the Planula to the attainment of the Adult 



Form . . . . .89 



Development by Actinulse . . . .90 



3. Significance of the Medusa in the Life-series of the Hydroid . 93 



Direct Development of the Medusa from the Egg . . 98 



4. Relation between Zooidal and Embryonal Multiplication in the 



Hydroida ; Polymerism and. Heteromorphism ; Genetic Suc- 

 cession of Zooids . . . . .101 



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