532 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the rudiments of many organs and tissues united into an apparent 

 whole. On the other hand, the mesothelium or coelothelium is phylo- 

 genetically a primitive organ, similar to the ectoderm or endoderm, and 

 originated in the germ-cells of the primitive multicellular animals. In 

 •consequence, the author rejects entirely Faussek's theory that the 

 secondary body-cavity had primarily an excretory significance ; it was 

 primarily a space in which the genital products originated and ripened. 



Notes on Dybowscella baicalensis. — W. Zykoff* notes, in regard 

 to this interesting form described by Prof. J. Nusbaum from Lake 

 Baikal, that it is not the first recorded fresh-water Polychaete, and that it 

 may have been described before. For in 1858, Prof. Jos. Leidy found 

 in the Schuylkill River, at Fairmount, Philadelphia, a small Polycbaste 

 which he named Manayunhia speciosa. A comparison of Leidy's de- 

 scription and figures with those given by Nusbaum leads Zykoff to 

 conclude that the Baikal form belongs to the genus Manayunhia, and 

 probably to the same species. This would be interesting as an instance 

 of discontinuous distribution. 



Nusbaum | expresses his pleasure at learning from Prof. A. Giard 

 that Dybowscella baicalensis does not stand alone. Besides Leidy's 

 Manayunhia speciosa, there is A. G. Bourne's Eaplobranchus sestuarius 

 from brackish water (1883), and Giard's Caobangia billet from fresh- 

 water in Tonkin. Nusbaum notes that Caobangia and Manayunhia are 

 hermaphrodite and have green blood, while Dybowscella has the sexes 

 separate and has colourless blood ; and there are other differences. 

 After some reference to Polychfetes from brackish water, e.g. Nereis 

 •diver sicolor, Nusbaum has a little to say about the exceedingly charac- 

 teristic structure of the Nephridia in Dybowscella, which have some 

 resemblance to those in Chaetogastridre and fresh-water leeches. 



Structure and Habits of Ammoeharidae.^— A. T. Watson has ma !e 

 a series of observations on Owenia, both native and Mediterranean speci- 

 mens, with special reference to the tube and tube-building. The tube 

 consists of an internal tough translucent sheath, prolonged forward 

 into a cone bearing a minute aperture at its tip, and an investment of 

 fragments of shell and stone. The fragments are free from une 

 another, and are attached by one side only to the tube, which in certain 

 stages of contraction gives the characteristic imbricated appearance. 

 The animal is nocturnal, but not, as has been supposed, exclusively 

 sedentary ; it is capable of a considerable amount of movement, carry- 

 ing its tube with it. The metastomium (Lippenorgan) is of great im- 

 portance in tube-building, and supplies the cement by means of which 

 the foreign particles are attached to the translucent sheath. The sheath 

 itself is formed by the secretion of the thread-glands. Among other 

 results obtained by the research, the author finds that the cephalic lobe 

 has an opening to the exterior, a phenomenon found in some Olio-o- 

 chajtes, but not hitherto described in Polychaetes. Further, it was found 

 that the spermatozoa leave the body by two tubular openings on the 

 ventral wall of the anal extremity ; the male protrudes some 20 mm. 

 of the body from the tube at the time, so that dispersion is relatively 



* Biol. Centralbl., xxi. (1901) pp. 269-70. t Tom. cit., pp. 270-3. 



; Journ. Linn. Soo. (Zoo!.), xxviii. (1901) pp. 2:^0-60 (3 pis.). 



