ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 533 



Nannoplankton of the Lake of Zug.* — Kurt Lantzsch has made 

 a study of biological conditions of the Lake of Zug, with special reference 

 to the nannoplankton and its relation to the zooplankton in deep lakes. 

 The nannoplankton shows a characteristic layering in summer and 

 autumn. At these seasons the lower limit of the occurrence of the 

 nannoplankton is about 80 m. Its representatives at these depths 

 consisted of Schizophycese (?) (Chroococcus and Gomphosphseria) and 

 diatoms (Cyclotella:). The Flagellates (Chromulina ovalis) seem to be 

 confined to the upper 40-50 m. They show active phototactic migra- 

 tions. Towards autumn the optimal zone of the components of the 

 nannoplankton becomes more marked, and is specific for each type 

 (Chroococcus, Gomphosphseria, Binucharia, Cyclotellae). It is apparently 

 determined by the transparence and by the quantity of light at the time. 

 The winter convection-currents break up this layering and a distribution 

 of the nannoplankton takes place, so that it extends without a well-defined 

 maximum, from the surface to the bottom (0-200 m.). In May the 

 summer boundary of 70-80 m. is again observable. In regard to the 

 zooplankton, the author confirms Burckhardt's dictum that the distribu- 

 tion of Copepods, Cladocera, and Rotifers depends on the presence of a 

 food-supply in solid form. The depth-limit of the Copepoda undergoes 

 the same seasonal changes as that of the food-supply. Light changes 

 determine the daily migrations of the Copepods, Cladocera,.and Rotifers, 

 a change in transparence corresponding to the change in the maximal 

 depth-limit of Rotifers. The maximal accumulation of Rotifers at a 

 particular level seems to be conditioned by intensity of light rather than 

 by abundant food, and it is specific for the different forms of pelagic 

 Rotifers. 



Plankton of the Mansfeld Lake.j — F. V. Colditz has made investi- 

 gations, extending over eighteen months, into the biological conditions 

 of the Mansfeld Lake, with special reference to the nannoplankton and 

 its relations to the zooplankton. He finds that in this lake, which is of 

 medium depth, there is a direct relation between the distribution of 

 nannoplankton and the food-supply, and that light and wave-motion 

 have also a direct influence on distribution. The quantity of nanno- 

 plankton directly determines the quantity of Copepods, etc. Details as 

 to the physical and chemical conditions of the water, and of the com- 

 position of the zooplankton and nannoplankton, are given. 



Tunicata. 



Fertilization in Phallusia.J — Fr. Meves has investigated the 

 fertilization of the ovum in Phallusia wafnillate with particular reference 



to what happens to the plastosomatic portion of the spermatozoon. He 

 gives an account of the structure of the spermatozoon, which shows a 

 plastosomatic tubular sheath surrounding the median part of the head. 



* Zeitschr. wiss. Zool., cviii. (1914) pp. 631-92 (6 figs.). 



t Zeitschr. wiss. Zool., cviii. (1914) pp. 520-631 (1 map and 32 figs.). 



% Arch. Mikr. Anat., lxxxii. (1913) 2te Abt., pp. 215-60 (4 pis. and 7 figs.). 



