CONTENTS. 
I. INTRODUCTION, . . . 
II. MORPHOLOGY— 
1. General Structure. — T he Rhagon; Types of Chamber-System, Eurypylous, Aphodal, 
and Diplodal j Ectosome and Choanosome; Suhdermal and Subcortical Cavities. Types 
of Canal System ; the Oscule and Pores ; Secondary' Canals or Epochetose System, 
2. Histology. — C ollenchyme and Collencytes, Sarcenchyme and Sarcencytes, Cystenchyme, 
Chondrenchyme, Thesocytes, Chromatocytes, Inocytes, Myocytes, Aisthocytes, Proto- 
plasmic Continuity, Scleroblasts, Genital Products, . . . . . 
3. The Skeleton. — S keletal Elements, Opal, and Spongin ; Spicules, Structure, Classifica- 
tion, Ontogeny, Phytogeny, .^Etiology of Spicules ; Types of Arrangement ; Extrusion 
of Spicules ; Source of the Silica of Flints, ...... 
4. Ontogeny, .......... 
5. Classification. — P osition of the Sponges in the Animal Kingdom, Subdivision into 
Classes ; Classification of the Tetractinellida ; Description of Families and Genera, . 
6. Note on Phylogeny, ........ 
7. Methods op Investigation, ........ 
III. DESCRIPTION OF SPECIES— 
Order I. Choristida, . . . . . . . . . 
Suborder I. Sigmatophora, ........ 
Family I. Tetillidae, ........ 
Tetilla, O. Schmidt, ....... 
Chrotella, Sollas, ....... 
Cinachyra, Sollas, . . . . . . 
Craniella, O. Schmidt, ....... 
Supplementary Account of Tetillidse not in the Challenger Collection, 
Tetilla, ......... 
Craniella, ........ 
FangopMlina, O. Schmidt, ...... 
Tabular View of the Tetillidse, ...... 
Family II. Samidse, . . . . 
Samus, Gray, ........ 
Suborder II. Astrophora, ........ 
Demus I. Streptastrosa, ........ 
Family I. Theneidae, ........ 
Thenea (Gray), ........ 
Pcedllastra, Sollas, ....... 
Sphinctrella, 0. Schmidt, ...... 
Characella, Sollas, ....... 
Triptolemus, n. gen., ....... 
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