ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 597 



Labrus merula. It is very favourable for a study of early stages, since 

 the egg has no shell and has very large cells. We cannot do more than 

 refer to three points. There is no trace of true yolk-cells, and the 

 early nutrition of the embryo must be exclusively from the uterine 

 wall. The enveloping membrane is formed from cells contributed by 

 the equivalent of the yolk-gland. In the maturation there is no pseudo- 

 reduction ; there is the normal number (not half the normal number) 

 •of chromosomes in the nucleus, and there is separating off of entire 

 chromosomes in the second maturation division. 



Oogenesis and Development of Fasciola hepatica.* — W. Schubmann 

 describes the development of the oocytes in the ovarian csecal tubes, 

 their connection to the wall by a nutritive stalk, their discharge into 

 the oviduct, and the degeneration of a large number into nutritive 

 material. The history of the yolk-cells is followed : 28-30 surround 

 each ovum. The egg-shell arises by direct differentiation from the 

 shell-gland secretion which envelops the ovum and its companion 

 yolk-cells. 



Maturation sets in after the formation of the egg-shell, after the egg 

 has reached the beginning of the uterus. Three polar bodies are 

 formed. The spermatozoon enters during the formation of the first 

 polar body. The egg remains in the uterus till the two resting 

 pronuclei are formed ; the further changes occur after the eggs are 

 liberated. 



Segmentation leads to the formation of a macromere and several 

 micromeres, which divide actively and surround the former. Mean- 

 while the yolk-cells disrupt within the shell and furnish nutriment for 

 the growing embryo. The ensheathing membrane is of embryonic 

 origin from liberated ectoderm cells, and not a product of the yolk-cells. 



Planaria alpina in Belg-ium.t — L. Fredericq has found this 

 characteristic Alpine Planarian on the plateau of Baraque-Michel, 

 within the Belgian frontier. It is a new acquisition for the Belgian 

 fauna. 



Eumesostominse.! — Alex. Luther has worked through a large 

 number of these fresh-water Turbellarians, and gives a connected 

 account of their structure. He recognises three tribes : I. Olisthanellida, 

 including the genus Olisthanella Voigt ; II. Typhloplanida, including 

 Strongylostoma Oerst, Rhynchomesostoma, g. n., Tetracelis Hempr. and 

 Ehrenb., Castrada 0. Schm., Typhloplana Hempr. and Ehrenb. ; 

 III. Mesostomida, including Mesostoma Oerst and Bothromeso stoma 

 Braun. 



Development of Fresh-water Dendrocoela.§ — E. Mattiesen has 

 studied Planaria torva and other forms, with especial reference to the 

 formation and contents of the cocoon, flie maturation of the ovum, the 

 changes in the segmentation-nucleus leading on to the first mitosis, and 

 the early stages in development. We cannot do more than refer to one 



* Zool. Jahrb. xxi. (1905) pp. 571-606 (2 pis.). 



t Bull. Classe Soi. Acad. Belg., v. (1905) pp. 199-200. 



% Zeitschr. wise. Zool., Ixxvii. (1904) pp. 1-273 (9 pis. and 16 figs.). 



§ Tom. cit., pp. 274-361 (4 pis. and 3 figs.). 



