472 SUMMAEY OF CUEBENT EESEAECHES EELATING TO 



Porifera. 



New Sponge Pigment.* — Dr. C. A. MacMunn has investigated the 

 characters of the purple pigment of Suberites wilsoni, an Australian 

 sponge. The pigment is soluble in dilute acid and dilute alkaline solu- 

 tions, and gives a banded spectrum. It is very stable, and can be readily 

 obtained in a fairly pure condition. Its relations and constitution have 

 not yet been made out. 



Later Development of Sycons.f — Dr. Otto Maas set before himself 

 a double problem in reference to the development of Sycons : — (1) the 

 conversion of the larva after fixation into the functional sponge in its 

 simplest Ascon form ; (2) the conversion of the tubular Ascon into the 

 complicated Sycon. As the hitter process is slow, the two could not 

 be followed in the same species ; Sycandra setosa therefore formed the 

 object of the first investigation, and S. raphanw of the second. As to 

 the first point, sections confirmed Schultze's observations on the meta- 

 morphosis, and showed the continuity of the two cell layers through the 

 metamorphosis. The dermal cells divide by a mitotic process to produce 

 small cells from which the first spicules arise. Further differentiation 

 occurs among the dermal cells ; and as the little sponge becomes dis- 

 tended the following kinds of elements become obvious : — 



(a) Belonging to the gastral layer : 



(1) Collar cells. 



(6) Belouging to the dermal layer : 



(2) Epithelial covering cells. 



(3) Pore-cells. 



(4) Spicule-cells. 



(c) Belonging to no germinal layer : 



(5) Wandering amoeboid cells which become genital cells later. 

 By the opening of the pores the sponge then reaches the functional 



Ascon stage. 



In the process of conversion of such an Ascon into a Sycon, the 

 Sycon tubes appear in a circle about the middle of the sponge, and this 

 first circle is followed by others. As the tubes grow out from the 

 central cavity, the collar-cells, as is well known, become confined to the 

 tubes, and the central cavity between the tubes is lined by the flattened 

 cells which constitute the so-called gastral membrane of authors. This 

 " gastral membrane " is, however, not produced by a modification of 

 gastral cells, but is due to the ingrowth of dermal cells, which push 

 themselves inwards from the exterior so as to interrupt at regular 

 intervals the original continuity of the gastral layer. This position is 

 supported by some admirably clear figures of sections. 



Collar-Cells of Sponges.* — Fr. Zemlitschka has investigated the 

 question whether the collar-cells of sponges actually take up solid par- 

 ticles, and if so, what becomes of the particles. He finds that in 

 Sycandra raphanus it is the collar-cells only which take up particles 

 suspended in sea-water. If the particles be indigestible, e.g. particles 

 of carbon, they do not give them up to the cells of the intermediate 



* Quart. Journ. Micr. Sci.. xliii. (1900) pp. 337-49 (1 pi. and 2 charts). 

 + Zeitschr. wiss. Zool.; lxvii. (1900; pp. 215-46 (4 pis.). 

 t Tom. cit., pp. 241-6 (2 figs.). 



