204 PORIFERA 



uniting in trunks and these in turn lirancliing to go to the ampulln?. 

 The exeurrent canals also sliow a similar tree-lilce arrangement. Not 

 infrequently extensive sulnlermal or sulicloacal spaces occur. The 

 relations may be more compHcated by the development of several 

 cloaca', or by the brandling of the sponge (fig. 

 104), while still further the ])ranches may 

 anastomose (lig. 1O5), gi\ing rise to a network. 

 Sponges may reproduce asexually, small 

 portions separating as Ijuds and producing new 

 animals (I'lg. 88). Usually sexual reproduction 

 prevails. The eggs, which like the spermatozoa 

 arise from mesoderm cells (lig, 160), undergo 

 segmentation and leave the parent as llagcllate 

 larva? (fig. 166, ^4). At fixation a kind of gas- 

 trulation takes place, the lilastopore {B) closes, 

 and the osculum, an entirely new formation, 

 arises at the opposite pole. 



The sponges arc frequently regarded as Coe- 



Pif, jQ^, Development lenterata, but scarcely a single homology can be 



of Sycandra raphamis (after drawn between the two. The ccrlcntcrate mouth 

 Schulze). .1 blastula; B, is diifercnt from cither pores or oscula. Indeed, it 

 gastrula at the moment of is disputed whether the collared cells are entoderm, 

 fixation; ck, cctomesoderm; }i[ost sponges possess a skeleton secreted by special 

 en, entoderm. mesoderm cells, and this skeleton atTords ihc 



means, according as it is composed of calcic car- 

 bonate or of silica, of dividing the sponges into two classes, besides, there are 

 two groups, Ceraospongia: and Myxospongi;e, in which the skeleton is res]>ec- 

 tively of horny substance (spoui^iii) or is lacking entirely. These seem to be 

 descendants of the silicious forms. 



Order I. Calcispongise. 



The calc sponges are exclusively marine and mostly live in shallow water. 

 They are grayish or white in color, of small size, rarely exceetling an inch in 

 length. The skeletal spicules usually project through the epithelium, forming 

 silky crowns in the neighborhood of the osculum. One-, three-, and four-rayed 

 spicules arc recognized, these ground forms presenting by iniequal development 

 a great variety of shapes. 



Sub Order I. ASCONKS. Thin porose walls and central 'stomach.' 

 Lcucosoiciiia/''- Sub Order II. SYCONES. Cloaca present surrounded by 

 ampulK-e radially arranged. CniHlia* Sycoii* Sycandra * Suh Order III. 

 LEUCONICS, .\ com|)licateil system of branching canals in thick walls 

 connects the ampulke with outer siui'ace and cloaeal cavity. Lciiiiita,LiU(oiiis. 



Order II. Silicispongiae. 



The siliceous sponges are richest in s])ecics and occur at all depths of the 

 sea, being fre(iuently noticeable from their size and bright colors. They are 

 subdivided into Triaxonia and Tetraxonia. In the Triaxonia the s]>icules 

 composing the skeleton — a|.)pearing as if of spun glass (hence Hyalospongia, or 



