ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 6: '.9 



posite Ascidians. He has previously referred to similar phenomena in 

 Botryllids. The beating goes on after all the organs of the ascidio- 

 zoids have undergone advanced degenerative histolysis, and it begins 

 precociously in the young zooids before these (which have an interesting 

 triple origin) are as yet integrated into a continuous whole. 



Development of Molgulidse. * — D. Damas has studied the embryos 

 of Lithonephyra eugyranda, Molgida echinosiphonica, and Anurella blcizi. 

 In connection with the cleavage of the ovum, he notes the occasional 

 occurrence of multiple division-figures, most numerous towards the 

 periphery, within an undivided protoplasmic mass. An account is 

 given of the development of the notochord, " muscle "-plates, and 

 neural tube in the early embryo ; and the author corroborates what 

 Lacaze-Duthiers observed in regard to the remarkable caudal degenera- 

 tion which leads to the " anurous " embryo. 



The larval nervous system, well developed in many Ascidians, does 

 not advance far in the Molgulidse studied. It begins to dwindle after 

 the outlining of three chief divisions, — the cerebral vesicle, the visceral 

 region, and the caudal portion. There are never any sense-organs in 

 the anurous larvas, but the urodelous forms have a single pigmented 

 cerebral organ. The greater part of the primitive neural canal is de- 

 stroyed in the retrogressive metamorphosis. The relations of the 

 hypophysis with the epiblastic portion of the mouth, and the communi- 

 cation of hypophysial tube and neural canal, are very distinct. 



There is a simultaneous formation of two pairs of branchial stig- 

 mata. The parietal wall of the peribranchial cavity is formed by the 

 epiblastic layer, while the visceral wall includes, on the one hand, the 

 lips of the stigmata formed by hypoblastic diverticula, and on the other 

 hand, an interposed cellular column of epiblastic origin. 



A solid rudiment, median and symmetrical, gives origin to the renal 

 vesicle. The pericardium passes in its development through a stage 

 when it appears as a compact mass. These two organs are both formed 

 at the posterior end of the endostyle, and their development extends 

 through a considerable period of embryonic life. 



INVEBTEBHATA. 



Variations of Plankton in Lake Geneva.! — E. Yung, in continuing 

 a previous investigation, indicates very strongly that the methods in 

 vogue for measuring quantitative variations in plankton are inadequate. 

 Hasty generalisations as to seasonal variation, based on insufficient data, 

 are doing much more harm than good. 



Mollusca. 

 a. Cephalopoda. 

 Amphitretus from the Sagami Sea4—L Ijima and S. Ikeda de- 

 scribe a specimen of this remarkable Octopod— a member of a rare and 

 interesting genus — perhaps identical with the single species as yet 

 known A. pelagicus, described by Hoyle. 



The authors agree with Hoyle in regarding Amphitretus as a repre- 



* Arch. Biol., xviii. (1902) pp. 599-664 (4 pis.). 



f Arch. Phys. Nat., xiv. (1902) pp. 119-31 (1 pi.). 



X Armot, Zool. Japon., iv. (1902) pp. 85-101 (1 pi. and 3 figs.). 



