ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 423 



species, giving all the characters — shape of jaws, number of flame-cells, 

 and shape of male — by which it can be distinguished from closely allied 

 species, and comparing these characters with those of A. brightwelli and 

 A. amphora. A plate with figures of the jaws of these various forms 

 and of the males accompanies the paper. 



New Rotifers. — F. R. Dixon-Nuttall * describes a new species, 

 Diaschiza ventripes, which is characterised principally by the ventral 

 position of the foot and toes. Two very good figures accompany the 

 paper, as well as a very useful key for the identification of the other 

 species of this difficult genus. 



M. F. Dunlop f has a short account of Catlujpna llgona sp. n., which 

 he discovered in Scotland, and which is distinguished by a broad spade- 

 shaped appendage to the ventral plate. By means of the good figures 

 accompanying the description this new form can always be readily 

 identified. 



Echinoderma. 



Polarity in Egg of Sea-urchin. £ — Prof. Th. Boveri finds that the 

 mature egg of Strongylocentrotus lividus shows a division into three 

 regions, each of which gives rise to a special part of the future embryo. 

 The animal and vegetative halves of the egg are separated by a pig- 

 mented zone ; this pigmented zone gives rise to the gut and its deriva- 

 tives ; the vegetative pole to the primary mesenchyme and the larval 

 skeleton ; the animal jjole to the ectoblast and its derivatives. The 

 author does not regard the morphological difference as the cause of 

 this difference in development, but as merely the expression of a pre- 

 existing physiological distinction. As to the exact nature of this in- 

 trinsic polarity, the author is inclined to lay stress upon the differences 

 between the animal and vegetative regions of the egg, as determining 

 the developmental processes. He explains the production of normal 

 plutei from (a) separated blastomeres, or (6) two united eggs, as due to 

 the fact that the segmented egg is not a unity, but a collection of in- 

 dividuals, which later lose their individuality in building up a unity 

 of a higher order. Normal development consists in this loss of in- 

 dividuality by the units in order to constitute a new complex indi- 

 viduality. 



Coelentera. 



Origin of Reproductive Organs in Ctenophora.§ — A. Garbe has 

 studied this iu Pleurobrachia rhodopis and PI. pileus. The formation 

 of the meridional vessels occurs by progressive splitting from the 

 aboral end towards the sensory pole, and not by a series of independent 

 buddings from the funnel. All the eight ribs are present in the youngest 

 larva?, which have only two main meridional vessels. The germ-cells 

 arise in the oral ends of the meridional vessels by proliferation of the 

 walls of the vessels, and increase in size towards the sensory pole. 

 They do not protrude into the lumen of the vessels, but occur in the 



* Journ. Quek. Micr. Club, viii. (1901) pp. 25-8 (1 pi.). 



+ Tom. cit., pp. 29-32 (1 pi.). 



X Verb.. Phys. Med. Ges. Wiirzburg, xxxiv. (1901) pp. 145-76 (4 figs.). 



§ Zeitechr. wiss. Zool., lxix. (1901) pp. 472-91 (2 pis.). 



