10 Sposig . SPONQLE. 
remainder of the work is comparative ; the general ontogeny of the 
Sponges is discussed, along with other theoretical questions. As regards 
the systematic position of the Sponges, the author states that “ their 
Coeleuterate nature, or their near relationship with the Gcelentera , is in 
no way supported by their developmental history. They are probably 
an independent phylum developed from the oldest Hcteroplastids by 
degeneration.” 
Goette (11) criticises some* of the conclusions arrived at by Heider. 
The disappearance of the ectoderm during development (Metschuikoff, 
Marshall, Schmidt, Goette), the isolated formation of flagellated cham- 
bers (Barrois, Keller, Goette), show that the ontogeny of Oscarella is 
not typical of Sponges in general. ’Even if all other of Heider’s conclu- 
sions be correct, it does not follow that the germinal layers of the Sponges 
can be liomologised with those of other Metazoa on Heider’s scheme. 
The flagellated epithelium of Sycandra proves by its origin and develop- 
ment that it is ectoderm. Heider determines the homology of layers, 
not by their origin, but by their- fate. Exceptionally in worms, an em- 
bryological separation of ectoderm into enteroderm and mesoderm fails 
( Accela , Dendrocoala ), or the ectoderm becomes lost ( Trematpdes , Gestodes): 
but in Sponges (except Oscarella) this is the rule ; they unite a want of 
differentiation with degeneration. 
Sollas (37) states that Heider is mistaken in supposing that the struc- 
ture of the embryos of Oscarella , observed by the former, can be 
explained by artificially produced wrinkling or shrivelling. 
Vosmaer (41) gives an account of our present knowledge of the onto- 
geny of Sponges; pp. 411-430. 
Physiology. 
Vosmaer (41) devotes a chapter to this subject ; pp. 4 51—445. 
Classification. 
Schulze (34) proposes the following classification of the Sponges and 
of the Hcxactinellida : — 
Type, PORIFERA. 
Class I. Calcarea. 
Class II. Non-Calcarea. 
Subclass 1. Ceratosa. 
Subclass 2. Silicea. 
Order 1. Monaxonia. • 
Order 2. Tetraxonia. 
Order 3. Triaxonia or Uexactinellida. Sponges with very loose soft 
body, in which isolated or siliceous spicules of the tri- 
axial type, or of reductions from this type, occur either 
' isolated or united into a solid framework by siliceous 
cement. 
