432 



NATURE 



[May 25, 191 1 



SOME RECENT WORKS ON A(2UAriC 

 ANIMALS} 



1) T~)K. TAhLllKK'S mono^rilph contains the 

 ment of observations in prudrcss on the 



tirst tnstal- 

 prugrcss on the biulo(<y of 

 this " Grossteich " — a lake situated about too km. north 

 of Prague. The present ntenioir, on the Chrysoinonads 

 (except the purely planktonic forms), deals with their 

 classification (two new genera and <-ight new species being 

 described), structure, motion, division, and encystment. 

 The occurrence of contractile vacuoles in Microglena and 

 of siliceous needles, as long as the cell, projecting from 

 the surface of Mallomonas, arc among the more note- 

 worthy features referred to. 



(a) The genus Ceratium is so common a constituent of 

 the fauna of many lakes and seas that an account of its 

 species, and the help offered in their more accurate identifi- 

 cation, will be welcome to workers on plankton. A short 

 account is given of the morphology and fission of C. tripos. 

 The genus is divided into four sub-genera, the armature 

 and relationships of which are examined. It is concluded 

 that the genus probably arose in temperate waters, and 

 spread thence into warmer and colder regions. There 

 are no known " bipolar " species. C. cornutum, one of 

 the three widely distributed fresh-wator species, seems to 

 be the oldest living s|)ecies and to stand nearest to the 

 hypothetical ancestor of the genus. The structural plan 

 of the fresh-water species suggests that they are primitive, 

 and that by migrations into the sea the marine forms have 

 arisen, and subsequently attained their great differentia- 

 tion. The author regards the heteromorphic chains dis- 

 covered by l.oiimann, in which the individuals at the two 



Vio. x.—H^-aloilaphnii <ncullata, from Fursee, Denmark. Note the 

 elongation of the cephalic shield in the indivicluaU taken in the summer. 

 The upper row of figures indicates the day and the month of capture of 

 specimens, tiie lo»cr row the temperature of the water (in degrees 

 centigrade). 



ends of the chain present more or less the characters of 

 two distinct species, not as normal, but as due to retro- 

 gressive phenomena ; possibly the reduced salinity of the 

 Baltic, in which they were observed, is responsible for 

 their formation. 



(3) Dr. Wesenberg-Lund gives an account of some of 

 the more recent work on fresh-water organisms, especially 

 of his own observations on the planktonic fauna of the 

 Danish lakes. He directs special attention to the varia- 

 tions in temperature, specific gravitv, and viscositv of the 

 waters of lakes at different periods of the vear, and points 

 out that, while the change in the specific gravity due to 

 temperature variation is insignificant, the viscosity alters 



' (1) Mono?raphien tind .VhhandUingen zur Internationalen Revue de 

 cesamten HyHrobiologie und Hydro?r.iphie. Band i, Heft t.— " De 

 Grossteich bet Hirschlwrg in Nord-Bohmen. 1. Cbrysomonaden aus dem 

 Hirschherger Grossteiche. Untersuchungen iiber die Flora des Hir«chberger 

 Grosste.ches^ '•../'«=''■ ^°" ^^- A Pascl.er. Pp. 66 + Tar. iii. (Leipzig : 

 Verlap yon Dr. Werner Klinkbardt, iqio). Price 10 marks. 



(a) Die Cetjtien. F.me k.irze Monographic der Gattung Ceratium 

 bchrank, von E. J-.reensen. Pp. iv+124 + Ta.x. (Uipzig : VerUg von 

 Dj- Werner Khnkhardt, 1911.) Price 11 marks 



(3) GrundzOge der B=oloeie und Geographic des Sfisswasserplanktons 

 nebst Bemerkungen fiber Hauptprobleme zukunftigcr limnologischer For- 

 ^hungen, yon Dr. Wesenberg-Lund. Pp.44. (Leipzig : Verlag von Dr. 

 WernerKlinkhardt. ipii.) Price 1.50 marks. 



(4) Biologi*che Studien an Lyncodaphniden und Chydoriden. von Dr. H. 

 Weigold. Pp. Ti8+Taf. x-xii. (Leipzig : Verlag von Dr. Werner Klink- 

 bardt, 1911.) Price 5 marks. 



(5) Studien und Experimente fiber die Eibildung und den Generation- 

 zyklus von Daphnia magna, von U. v. Scharfenberg Pp. 414-Taf. viii-f ix 

 ^ «l''xr^" .'..S "O" ^^- Werner Klinkhardt, 1911.) Price a marks. 



W Natural History of the Larvje of Donacina. By Dr A. G BiJving. 

 ^p. 108+plates vm. (Leipzig: Verlag von Dr. Werner Klinkhardt, loti. 

 Pnce 5 marks. " 



NO. 2169, VOL. 86] 



very considerablv. being, in fact, only half as much 

 25° C. as at o* C. lie conclude- •' • ^ ' ■ ' 

 this latter factor, ar< certain 

 l-"or instance, exampl. ^ <.f th< I < 

 taken in summer, « 

 shield, which has ; 



of gravity that, while ihc anjuial pi(.v>c.u>i> kwam aiji. 

 jHfrpendicularly, it now moves almost horizontally, ; 

 its resistance to falling is thus very considerably i:: 

 In the nearly related l^>smina the body is, in 

 higher than long, but in winter longer than h;^.. , 

 antenna; are twice as k)ng in sumi^r as in winter. 

 is pointed out that when the extent of these " !■ 

 poral '• variations is fully realised there will, r.< 

 be a great reduction in the number of r< 

 species. A further example of modification is gjv».!i- • 

 rotifer Asplanchna priodonta, the body of which is 

 winter subspherical, but in summer is about five times 

 long as broad, and approximately cylindrical, so that 

 the horizontal position be assumed in swimming, ■ 

 animal presents a greater resistance to sinking. ' 

 in the length and number of processes {e.g. C*r.! 

 an increase in the surface of organisms is 

 summer, correlated with the increased flotatic 



(4) Dr. Weigold 's account of the Lyncod.ic.i 

 Chydorids of Sa.xony contains much information r 

 the specific characters and biology of these Ci 

 details being given of the number of moults, the ': 

 life observed, locomotion, relations of the sexes, \ 



Fig. 2 — Ci'taiiiiiii /tiruntiimlla.As/ilanchna pruhiPit:!!. I'apnnia i-.^anf.a. 

 Hyalodafhnia tucullata and BomiiHa cortgoni (two races). I'ppcr 

 row; summer form< with incteased power of ftualin; ; lower ro* ; 

 winter forms. 



in form and numbers. The introduction of Chydorids ' 

 isolated waters is brought about almoiil exclusively ! 

 birds. The author has carefully worked out the breedir 

 seasons, and shows that, in the plains of centra) Europ 

 the Chydorids have two sexual periods, sometimes aim* - 

 confluent, but exhibiting maxima in July and October; : 

 more northerly reg'ons and in mountain waters th 

 maxima approach one another, and finally blend into a^ 

 single breeding period in August-September. 



(5) The work described in the fifth memoir was under* 

 taken in order to decide, by renewed obser\ations andl 

 experiments, whether the conclusions reached by Weis 

 mann or those of some of his critics are to be accepted. a 

 The main results go to show that Daphnia magna passes, i 

 during the course of a year, through several phases, butl| 

 the various generations and broods are not so sharply>: 

 circumscribed, in regard to the mode of their egg-forma-- 

 tion, as Weismann believed. The author states his views 

 of the sequence of phases thus : — resting egg — strong ^ 

 tendency to parthen<^enesis — waning of parthen<^enesi» 5 

 and increased tendency to sexual reproduction — strong ; 

 tendency to sexual reproduction — resting egg. The par- f 

 thenogenetic and resting eggs, the genesis of which i»^ 

 traced, differ from one another, not only in number and § 

 in nature of yolk and shell, but also in mode of forma- 

 tion ; each of the former arises from a group of four cell 

 one of which becomes the egg, while the other three ar 



