The porifera and coelentera . s = So >> ^ O c bi ^^ o 3 tJ *§ 0 po .5 o O « Cm S 03 09 03 — J— CO d o ^ rt s o o s ps ? •c o c g ?Z S b 5 3 o ;4 <i PU ^ 00 ?^ ? m -^^ :- M ^ ^^ o ^ ^ lit -U O ^ 2 S2 .2 ^ ^?^ •g •c PE< C s ^ 1 X ,0 \ a \ H \ \i l\i M O immigration of cells takes place at any point. When there are no pos-terior granular cells, however, the iinmij^rntion may be entirely restrictedto the posterior pole, so that the hinderinost flagellated cells become con- SPONGES 75 tinually modified and pass iuto the interior, their place being filled bythe closing in of the cilia
The porifera and coelentera . s = So >> ^ O c bi ^^ o 3 tJ *§ 0 po .5 o O « Cm S 03 09 03 — J— CO d o ^ rt s o o s ps ? •c o c g ?Z S b 5 3 o ;4 <i PU ^ 00 ?^ ? m -^^ :- M ^ ^^ o ^ ^ lit -U O ^ 2 S2 .2 ^ ^?^ •g •c PE< C s ^ 1 X ,0 \ a \ H \ \i l\i M O immigration of cells takes place at any point. When there are no pos-terior granular cells, however, the iinmij^rntion may be entirely restrictedto the posterior pole, so that the hinderinost flagellated cells become con- SPONGES 75 tinually modified and pass iuto the interior, their place being filled bythe closing in of the ciliated layer. Thus three types of iiarenchynmlaecan be distinguished in the Clathrinidae, which may be tabulated asfollows :— Posterior Granular Cells. 1. Present 2. Absent:i. Absent (Ex. CL blanca).-Multijiolar (Ex. CI. cerebrum]Unijiolar ^Ex. CI. reticulum).. Types of sponi,f larvae, diagrammatic; tlie ciliated cells are left clear, the deniial cells(inner mass) are shaded, the archaeocytes are granulated. Transformation of ciliated (gastral)into dermal cells is represented by graduated shading. 1, larva of Clathrina reticulum ; 2,newly-hatched larva of (or pseudo-gastrula stage of .Si/coii); 3, late larva of (or newly-hatched larva of Sycon); 4, lar\a of Oi^nmlla (^ter Maas); archaeocytescoiyectiiral; 5, larva of Mi/xilla (after Maas); 6, completely ciliated larva of a horny sponge ;SjKngilla is similar, but contains a cavity near to the anterior pole. The type of parenchymula larva exemplified by Clatlirinareticulum (Fig. 59, 1) affords an easy transition to the so-calledamphiblastula larva found in Leucosoleniidae, and in the greatmajority of Heferocoela. To understand the evolution of this typeit is necessary to sup])ose that in a normal parench3mula larva^vith archaeocytes placed internally, and with immigr
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
