10 Porifera. 



the older branches this structure is inextricably confused. The author observes 

 that the spicules of Petrostoma are not cemented together by extraneous matter, as 

 in the fossil Pharetrones [but see infra, Rauff (*)], but actually fused as in the 

 Lithistida and Dictyonina. [G. P. Bidder]. 



Rauff (') believes that the fossil Calcaria do not differ so much from the 

 recent representatives as is generally accepted. The fibres of Pharetrones he 

 considers to be a product of fossilization. His new sub-family Polysteganinae 

 are in fact belonging to the Syconidae. The more striking difference with recent 

 forms lies in the strange way of building colonies. They areSycons, bei welchen 

 kugelige oder niedergedriickt tonnenformige Einzeliudividuen perlschnurartig 

 aufeinander gesetzt sind. Next to this budding, there is a lateral outgrowing so 

 as to form larger colonies. As a type of the group, the author mentions the genus 

 Barroisia. No special cloacal skeleton, but a distinct dermal one, the latter being 

 made up from monaxons only. These are tylostyles, perhaps reduced tetraxons. 

 In the parenchyme, triads are frequent. The author is not sure whether also 

 tetrads occur. 



Dendy( 1 ) reproaches Lendenfeld his taking possession of the author's discovery 

 of the true nature of Teiclionidae without even mentioning the title of his paper on 

 the subject. Lendenfeld ( l ) defends himself, stating that he made the discovery 

 independently of Dendy. 



Lendenfeld ( 7 ) criticises Dendy's papers [see Bericht f. 1891 Porifera p 1] from 

 the systematic point of view and gives a tabular account of Dendy's species in refe- 

 rence to his own genera. 



II. Homocoela. 



Bidder (^ refers to his previous hypothesis [cf. Bericht f. 1891 Porif. p 7] that 

 the flask-shaped or glandular epithelium , which he believes to form the most 

 common external covering in all groups of sponges is excretory. This latter 

 proposition, so far as concerns Ascetta, may now be considered proved , since 

 under treatment during life with indigocarmine in sea-water the yellow granules 

 both of the Metschnikoff and ectoderm cells become replaced in part by dark- 

 blue granules, no other part of the sponge being in any way coloured blue. It 

 is suggested that the substance of these yellow granules is allied to spongin, and 

 that the spongoblasts of horny sponges are homologous with the cells of the flask- 

 shaped epithelium, the horny fibre, as supposed by Kolliker and others, with the 

 the cuticle. - - Basal spherules of the endoderm are described as of very different 

 reaction to the above; they are believed to be stores of nutritious matter. In 

 Heterocoela (probably it is similar in Silicea) the collars of the collar cells are at 



first mere fringes, which help to retain the food and filter the water When 



the cell is satiated the flagellum ceases to move, and degenerates ; the collar unites 

 with the neighbouring collars to prevent the water that is already filtered and 

 already foul from returning past the inactive area to pollute the afferent water 

 supply. When the food has been digested, the cells elongate and become closely 

 pressed together^ ; each cell then separates into a basal part (plinth) containing 

 the spherules and a nucleated distal part , the column . The columns then 

 start on a new cycle with hungry protoplasm, active flagella, and separated col- 

 lars. The author's previous statements as to metamorphosis of the Metschnikoff 

 cells are repeated, the hypothesis is suggested that primitively the afferent pores 

 of sponges are perforated excretory cells derived from the endoderm, while the 

 ectoderm is a layer of cells excreting constantly from the intercellular jelly. 



