Porifera. 



Hircinia is kept, on account of the filaments being a part of the skeleton and not 

 parasites, but it is stated that the well-known threads also occur in other sponges, 

 e. g. Spongelia herbacea n. sp. Lendenfeld ( 3 ) believes now that the Horn- 

 schwamme keine monophyletische Thiergruppe darstellenw. 



According to Lendenfeld ( 6 , 2 ) sponges arise from Protozoa like the Choano- 

 flagellata, but most probably they are not of the same stock as any of the other 

 Metazoa. Porifera and Cnidaria have been developed from a sac-shaped an- 

 cestral form with simple ectoderm, simple entoderm and undifferentiated cells in 

 the intervening mesogloea. Arising from this the stem of the sponges divides 

 dichotomously into two equivalent branches, represented by the Calcarea and 

 Silicea. This old division is thus accepted by the author, but further divisions are 

 rather altered by distributing the Horny Spongestc amongst them [cf. below, p 6, 7] . 

 In both the development from the ancestral free-swimming form, viz. the formation 

 of ciliated chambers, and the fixing of the axis and rays of the spicules, were the 

 same. The primordial Silicea had indifferent irregular spicules, from which the 

 triaxon and the tetraxon spicules were developed by an adaptation to the diver- 

 gent development of the canal systems. Following these views and those of other 

 authors, a classification of Porifera is given, by no means, however, entirely new. 

 In this, sponges form the phylum of the Mesodermalia, i. e. Coelentera with 

 traversing canal system, and organs developed from cells of the mesogloea or pri- 

 mary mesoderm. With collar cells ; without movable appendages. Two classes: 

 Calcarea and Silicea. The former class is divided into Polejaeff's Homocoela and 

 Heterocoela. The latter class as follows :. Sub-classis 1. Triaxonia. Silicea with 

 simple canal system, large sac-shaped wide-mouthed chambers, slightly developed 

 mesogloea, and a skeleton composed of triaxon siliceous or rarely horny spicules 

 or pithed horny fibres ; rarely without skeleton*. Two orders : Hexactinellida and 

 Hexaceratina [cf. infra, p 7]. Sub-classis 2. Tetraxonia. Silicea with a com- 

 plicated canal system, small spherical or oval chambers, and well-developed meso- 

 gloea ; with a skeleton composed of tetraxou or monaxon megasclera, or a network 

 of horny fibres, with or without proper spicules ; rarely without a skeletons Two 

 orders : Chondrospongiae and Cornacuspongiae. The Chondrospongiae are divided 

 into four sub-orders: Sollas' Lithistida and Choristida (to which a new group, 

 Megasclerophora, is added), and Vosmaer's Clavulina (in which are included the 

 Spongillidae) and Oligosilicina. The Cornacuspongiae as follows : Fam. 1 

 Desmacidonidae. 'Cornacuspongiae with a supporting skeleton composed of a 

 network of spicule-bundles, cemented together by spongin. Microsclera usually 

 present: chelae, to which other meniscoids may be added ; when chelae are absent, 

 the fibres of the supporting skeleton are echinated by proper spicules. Fam. 2. 

 Aulenidae [cf. infra, p 7]. Fam. 3. Heterorrhaphidae. Cornacuspongiae with 

 a skeleton composed of a network of spicule-bundles cemented together by spongin 

 and never echiuated. Microsclera usually present : sigmata, diancistra, toxa or 

 trichodragmata ; never chelae*. Fam. 4. Spongelidae [cf. infra, p 7]. Fam. 5. 

 Homorrhaphidae. Cornacuspongiae with a skeleton composed of spicule-bundles, 

 or scattered oxeote, more rarely stylote, megasclera cemented with spongin. 

 Without microsclera, except rarely toxa. Fam. 6 Spongidae [cf. infra, p 7], 



Haeckel cannot agree with the view that Ceratina are descendants from true 

 Silicispongiae, and proposes the following Classification of Sponges : - Class 1. 

 Protospongiae (with tubular canal-system) : Order 1 . Ammoconidae = Cannocoela, 

 Order 2. Asconidae = Homocoela. Class 2. Metaspongiae (with vesicular canal- 

 system): Order 1. Malthospongiae = Domatocoela, Order 2. Demospongiae, Order 3. 

 Hyalospongiae, Order 4. Calcispongiae = Heterocoela. - - See also infra Coelente- 

 rates, p 2, Hatschek. 



