. Elementary text-book of zoology [electronic resource]. Zoology. 2XVUFERA. 109 In these four types there will be noticed a progressive in- crease in bulk of the body of the sponge and a progress of the choanocytic a?'eas from within outwards. Numerous transi- tion types are found, and these types are distributed quite indiscriminately throughout the classes or orderr. Fir, 44.—Transverse Section of a Rhagon, (Diagrammatic).. Sponges fall into two^well defined classes, i. Calcarea. 2. Non-Calcarea. I. Calcarea.—The Calcarea all have a calcareous skeleton and the collared cells are much larger
. Elementary text-book of zoology [electronic resource]. Zoology. 2XVUFERA. 109 In these four types there will be noticed a progressive in- crease in bulk of the body of the sponge and a progress of the choanocytic a?'eas from within outwards. Numerous transi- tion types are found, and these types are distributed quite indiscriminately throughout the classes or orderr. Fir, 44.—Transverse Section of a Rhagon, (Diagrammatic).. Sponges fall into two^well defined classes, i. Calcarea. 2. Non-Calcarea. I. Calcarea.—The Calcarea all have a calcareous skeleton and the collared cells are much larger than those of the next class. They are usually Ascons and Sycons, and in many points they are simpler and more primitive than the No)i-caIcaira. 2. Non-Calcarea.—^In these the skeleton consists of ceratin (horny) fibres (with or without spicu]e>), siliceous spicules which may fuse, or there may be no skeleton. The collared cells are minute and the canal system is mostly Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Masterman, Arthur Thomas; Parsons, John Herbert, Sir, 1868-1957, donor; S. H. Lazarus (Firm); University College, London. Library Services. Edinburgh : E. & S. Livingstone
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