PORIFERA. III. 



which, according to the author, should be placed near to Histoderma; I cannot express myself more 

 particularly about this species, but its relationship with the forms here in question seems to me some- 

 what doubtful. 



The four genera mentioned are distiugushed among the Myxilleae by the megascleres being 

 the same in the dermal skeleton and in the skeleton of the inner body; this at all events holds quite- 

 good with regard to Histoderma, Histodermella and Inflatella; among the species of Cornulum it holds 

 also good for textile ; in singaporense and vesciculattim there are, to be sure, two forms of megascleres, 

 but they are both diactinal, and they seem not to be sharply divided with regard to their occurrence 

 in the sponge-body. The four genera are certainly nearly related to each other, and as their starting 

 point I think we may take Histoderma as most probable, which shows the least deviating structures; 

 as the genus nearest related to this I take In/latella, which, especially in the skeletal structure, presents 

 the greatest accordance, and on the whole mainly differs only in the want of microscleres, a 

 difference which, when the other structures agree, is of very slight consequence, indeed even 

 the right of Inflatella as a separate genus is perhaps doubtful, but at present I think, there is 

 some reason to keep it. Also Histodermella must be nearly related to Histoderma, one species, Ingolfi, 

 shows both in its exterior and in the skeletal structure great agreement; the curious, spined spi- 

 cules which are present in this genus, are somewhat surprising, but I think they must probably be 

 taken to have their origin from original special skeleton spicules. Cornulum stands a little more 

 apart, distinguished by its palmate chelae. — I thus take these four genera to be nearly related and 

 to represent a- type of Myxilleae in which the original skeleton spicules have disappeared. As said, 

 Histoderma might be thought to form the starting point; the genus outside the group, nearest related 

 to Histoderma, is perhaps Hymedesmia (= Leptosia Tops.); in several species of this genus we find a 

 strong dermal skeleton formed of diactinal spicules, and at the same time the inner skeleton, consisting 

 of the basal acanthostyles, may be very little developed; the acanthostyles may be present in so small 

 numbers, that great care is necessary to avoid mistakes, just in Hymedesmia-species of this latter structure 

 we find at the same time a strongly developed dermal skeleton which also has well developed fibres 

 going from the dermal membrane inwards, and here consisting of the same diactinal spicules which 

 form the dermal skeleton itself. Finally such species may have long, tubular papillae (e. g. Hymedesmia 

 filifera O. Schmidt, and several other species). — It is perhaps a question whether Histoderma phlycte- 

 nodes Cart will not prove to be a Hymedesmia. — When now such species get quite roundish and 

 grow without attachment, as e. g. H appendiculatum , the elimination of the acanthostyles is easily 

 understood, and the transition to the freely growing species is formed by such attached species as for 

 instance Histoderma physa. The genus Melonanchora seems to me to form a beautiful and interesting 

 instance of the opinions here advanced; one species of this genus has the spiculation and skeletal 

 structure typical for the Myxilleae. with skeletal styles and diactinal dermal spicules; these latter, 

 however, form a very dense dermal skeleton, and the species has oscular and pore-papillae; the other 

 species of the genus has a similar construction, but the skeleton spicules have disappeared and the 

 whole skeleton is formed of dermal spicules. 



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