BY R. VON LEXDENFELD, PH.D. 317 



Schmidt), and Monoctinellidae (Zittel.) From the whole extension 

 of this line or stem, branches take their origin, which are parallel 

 to one another and run in the same direction. Large at the 

 bottom, these branches taper towards the top ; they include 

 the Desrnacidonidae (small branch near the top.) Plakinidre, 

 Tetractinellidae, Lithistidse and the Hexactinellidre, two large 

 branches at the bottom, and some Sponges which ai'e allied to 

 the Ceraospongise, near the middle of the stem, but nevertheless 

 possesses flesh spicules. (Das System der Monactinella?, von 

 Lendenfeld and elsewhere.) 



We will return to this subject further on, under the heading 

 " Classification." 



II. — The minute structure of Sponges. 



As eveiy other Metazoan, the Sponge consists of a great many 

 cells, different in form and function ; and the products of these 

 cells. It appears cpiite logical to call the Sponge a colony of 

 Protozoa, but it must be borne in mind that every other Metazoan 

 is just as much a colony of Protozoa, as the Sponge. The latter 

 view is generally accepted, only that we do not call higher animals 

 colonies of Protozoa. 



The mass of the Sponge consists, like the Umbrella of the large 

 Medusae of connective tissue (Binclegewebe) 1 which may be of a 

 more gallerty or a more cartilage-like texture. It is to be 

 compared to the tissue which forms the umbilical cord known as 

 Wharton's galiert. This ground substance is in many cases 

 without visible structure, in others again it attains the characters 

 of fibrous tissue, and then the whole Sponge accordingly has a 

 tenacity like leather (Chondrosia.) 



In this ground substance we meet with cells and all the surfaces 

 of it are covered with Epithelia, so that the ground substance 

 comes in contact with the surrounding water nowhere. These 

 Epithelia are of a simple structure, and consist of one layer of 

 cells only. The muscular fibres are not in connection with 

 Epithelial cells, but produced from cells imbedded originally in 



