284 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Fresh-water Sponge from Sable Island.* — Dr. A. H. MacKay de- 

 scribes Heteromeyenia macouni n. sp. (possibly it will turn out to be 

 H. ryderi var. macouni *). It is especially interesting because of its 

 abundant occurrence (encrusting submerged stems of Myriophyllum 

 tenellum) in a pond or lake between the two parallel ridges of loose grey 

 sand which constitute Sable Island, in the Atlantic, nearly 100 miles 

 from Nova Scotia. 



Development of Sponge Spicules.f — Dr. Otto Maas has studied the 

 development of the spicules of a species of Tethya. There are three 

 kinds of spicule, the tylostyles, the chiasters, and the spherasters; all 

 originate in a single mother-cell, but, except in the case of the chiasters, 

 other cells take part in the growth and development. The spicule- 

 secreting cells are densely filled with grauulations, which originate with 

 the formation of the flinty substance. The chiaster-forming cells are 

 differentiated elements of the parenchyma, but the spherasters and tylo- 

 styles are formed in undifferentiated cells with vesicular nucleus and 

 nucleolus. The secondary formative cells arise partly by division of 

 the first formative cell, and are partly ordinary parenchyma cells. The 

 spherasters originate by the fusion of several small tetrasters, and the 

 further development takes place by the aggregation of fresh particles. 

 The tylostyles arise by the union of small irregular concretions within 

 a single cell, and the needle so formed increases by apposition through 

 the agency of epithelial formative cells. In their cells of origin, no less 

 than in the fact that they are completely formed by a single cell, the 

 microscleres or chiasters are sharply contrasted with the spherasters and 

 tylostyles. 



Protozoa. 



Reproduction of Radiolaria Tripylae.l — Dr. A. Borgert has suc- 

 ceeded in finding, among 20,000 specimens of Aulacantha scoly- 

 mantha, a sufficient number in the act of division to permit of a study 

 of the details of the process. He finds that cell-fission as well as the 

 formation of swarm-spores occurs, and in the process of fission the 

 nuclear division may be mitotic or amitotic. The present paper is con- 

 cerned only with the former process. In the prophase the reticular 

 chromatin of the resting stage forms a coiled thread. In the next stuge 

 this thread splits longitudinally and segments ; the segments again split 

 longitudinally, but the chromosomes so formed pass into the coiled con- 

 dition again before the formation of the equatorial plate. A remarkable 

 peculiarity is the enormous number (over 1000) of chromosomes, which 

 is to be regarded as an important point of contrast with Metazoan 

 mitosis, as is also the great variation in number of the chromosomes. 

 Other distinctions are the double longitudinal splitting mentioned above, 

 which occurs during a single division (contrast Ascaris, Salamandra, 

 &c), the absence of a true spindle, and the occurrence of a second coil- 

 stage after the splitting of the chromosomes. The occurrence of some 

 oi these at least the author is inclined to associate with the absence of 

 a sexual act. Of the many other observations contained in the paper, 



* Trans. Nova Scotian Inst. Sci., x. (1900) pp. 319-22. 

 t S.B. Akad. Wiss. Mlineken, 1900, pp. 553-69 (1 pi.). 

 j Zool. Jahrb., xiv. (1900) pp. 203-76 (5 pis. and 33 figs.). 



