810 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the species of the genus Mcycnia (Ephydatia), and to the same veil 

 as found between the spicules of SponyUla. This tissue, which consists 

 of airy cells (" cellules aeriennes "), acts as a hydrostatic apparatus, 

 which has attained a special development in the two forms above- 

 mentioned, Trochosp. erinaceus and Sp. Lordii. 



The freshwater European sponges may be grouped with reference 

 to the structure and development of their gcmmules : — 



I. Forms which produce ampbidiscs with toothed margins. 



(a) Disposed in a single stratum on the chitinous envelope, as 

 illustrated in a single species, Sp. fluviatilis (aut.), which M. Vejdowski 

 would regard as a distinct genus, Ephydatia. 



(b) Disposed in two strata, as illustrated in many forms with 

 slight differences, which may all be referred to the genus Meyenia. 



II. Forms which produce ampbidiscs united by their margins, as 

 represented in the single species Trochosp. erinaceus Vejd. 



III. Forms which produce spinose needles homologous with the 

 ampbidiscs. These are represented by a wholu series of flat ramified 

 sponges of variable size and form, but referable to a single genus or 

 even species of Spongilla, and by an unbranched form (Sp. fragilis 

 Leid.), for which a new genus might be erected. 



Vestibule of Dendrilla cavernosa.* — Under the heading of 

 " Studies on Sponges " Dr. E. v. Lendenfeld groups this and the three 

 following papers. 



This is a new species, remarkable for its laxity of structure. The 

 sponge is digitate ; tbc skeletal fibres dark brown ; oscula are never 

 found at the ends of the digitate processes. The whole sponge appears 

 hollow, the processes being cylindrical. This cavity or " pseudo- 

 gaster " has its walls covered with inhalent pores ; but no oscula are 

 present. Tbe pseudogaster is shut off from the water by the sub- 

 stance of the sponge ; there being a delicate perforated membrane at 

 the ends of the processes. 



At the breeding season the "pseudogaster" is occupied by the 

 embryos, wbich can escape and return through the pores in the 

 membrane. These pores can be dilated and contracted, and thus the 

 water current can be regulated. Tbe author derives this closed 

 vestibule from open ones by secondary folding, as is seen in Halme. 



The histological structure of the " vestibule membrane " is de- 

 scribed. Around each pore is a series of tangential muscle-cells, the 

 pore being surrounded by flat epithelial cells ; numerous peculiar 

 unicellular glands, like those described by the aiathor in Aplysillidae, 

 are found below the flat epithelium all over the membrane, forming 

 an incomplete ring round each pore. Inside the muscle-cells are 

 multipolar cells, which Dr. v. Lendenfeld regards as ganglia-cells, 

 and tbe spindle-shaped cells, between these ganglia-cells and the 

 edge of the pore, as nerve-cells. 



Gigantic Sponge. t — Dr. v. Lendenfeld regards Papillina 0. 

 Schmidt and Baphyrus Bower bank as distinct genera, and describes a 



* Proc. Linn. Soc. N. S. Wales, x. (188G) pp. 557-62 (1 pi.). 

 t Ibid., pp. 562-8 (3 pis.). 



