ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 399 



the osphradium, the nephridium, the nephridial gland, and the gonads. 

 A short account of the development is also given. 



5. Lamellibranchiata. 



Nephridia of Lamellibranchs.* —Nils Odhner has made a compara- 

 tive study of the nephridia in the families of Lamellibranchs, as regards 

 position, shape, communications, relations to gonads, and minute struc- 

 ture — a laborious piece of detailed comparative anatomy and histology. 

 He uses the nephridia as an additional criterion iu determining the 

 relationships of the different families. 



Minute Structure of Alimentary System of Fresh-water Mussel.f 

 Fritz Gutheil describes the epithelium, the musculature, and the con- 

 nective tissue of the alimentary tract of Anodonta cellensis Schrot., as 

 also the processes of secretion and absorption. The mid-gut gland or 

 "liver" is similarly discussed as to the epithelium of its tubules, the 

 ducts, and the connective tissue. The crystalline style of the intestine 

 is discussed at length, and regarded (with Mitra) as an active amylotic 

 ferment stored up in th j form of a flexiltle solid. 



Peculiar Degeneration of Germinal Vesicle in Mactra. % — K. 



Kostanecki describes a peculiar process in eggs which have been arti- 

 ficially induced to parthenogenetic development. Two polar bodies are 

 given off ; the segmentation spindle is formed ; but division goes on 

 without ovum-division. The nuclei usually coalesce and form in the 

 next mitosis a bipolar spindle. Large syn-karyonts result, one or two 

 in number in each ovum. Or bipolar mitosis may be seen with a very 

 large number of chromosomes. Or in some cases a large number of 

 small nuclei are seen in the ovum. In these cases there seems to be no 

 extension of polar bodies. The number of nuclei is usually twelve, 

 which is the normal number of chromosomes in the germ-cells of Mactra. 

 In these multinucleate ova, moreover, a persistent nucleolus is often 

 seen. It is probable that abnormal processes lead to the formation of 

 twelve nuclei from the 12 chromosome-groups which pass out into the 

 cytoplasm. 



Arthiopoda. 



a. insecta. 



Structure of Chordotonal Organs in Ants and Bees.§ — Arnold 

 Schon has made a detailed study of the minute structure of these 

 organs. The chordotonal organ in ants is firmly attached to the chitinous 

 wall of the leg by its long terminal fibres, which pass into club-shaped 

 cells. On the club-shaped cells there are seated cap-cells, and into these 

 the heads of the rods project. In each rod there is an axial nerve-fibre ; 

 this leads through the elongated enveloping-cell to a group of sensory 

 cells. These, again, are innervated by the subgenual nerve entering the 

 tibia from the femur. 



• Zeitschr. wiss. Zool., c. (1912) pp. 287-391 (40 figs.). 



t Zeitschr. wiss. Zool., xcix. (1912) pp. 444-538 (69 figs.). 



X Bull. Internat. Acad. Sci. Cracovie (1912) pp. 2.3-51 (2 pis. and 6 figs.). 



§ Zool. Jahrb., xxxi. (1911) pp. 489-72 (3 pis. and 9 figs.). 



