ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 487 



the gamete naturally pass into the developing soma, which, therefore, 

 shows the same variation as its parent did, even though removed from 

 the environment in question. (4) These substances may produce a 

 powerful effect, though present only in minimal quantities. (5) They 

 may be of such a nature as to stimulate the formation of antibodies, 

 thus causing a reaction in later generations. 



Development of Winter Eggs of Cladocera.*— C. Yollmer has 

 studied this in Daphnia magna and D. puJex. After at most four 

 intravitelline divisions cell-boundaries appear, and a total segmentation 

 is effected. This is completed at the 32-cell stage. The yolk is com- 

 pletely divided into pyramid-like cleavage-cells which meet in the 

 centre of the ovum. The result is like the result of holoblastic and 

 equal division in other cases — a blastula with a much reduced blastocoel. 



Then follows the formation of the central yolk-cells by multipolar 

 delamination of the cleavage-cells. The spherical yolk-cells become 

 close-packed in the interior, and are surrounded by the blastoderm-cells 

 which are also rich in yolk. 



While the blastoderm becomes more epithelium-like, a number of 

 cells migrate inwards from a narrowly limited area on the future ventral 

 surface. They form the primordium of the gonads. Shortly before 

 the resting stage is reached the apical plates are formed at the anterior 

 end as paired thickenings of the blastoderm. After the resting period 

 the lower layer is formed by polar immigration on the ventral surface, 

 the median streak forming the gut and the side wings the mesoderm. 

 The yolk-cells do not share in making the mid-gut. As external 

 segmentation begins the gonadial primordium forms the two ovaries. 



Varieties of Scapholeberis mucronata.f — Karl Gruber has analysed 

 some of the varieties of this Cladoceran, and makes it clear that in 

 order to distinguish between local modifications, seasonal dimorphism, 

 individual fluctuations, and elementary species, it is always necessary 

 to follow the animal from egg to adult. For there are many cases in 

 which the peculiarity, whatever it may be, is not manifested in the 

 young stages, but only finds expression in the course of growth. 



Crustacean Parasites of Annelids and Cephalodiscus.t — Ch. 

 Gravier gives full descriptions of some very remarkable forms : — (1) 

 HetyylloMus arcticus Steenstrup and Ltitken, a much degraded Copepod, 

 previously reported from the North, now described from Southern 

 Polycha^ts {Harmothoe spinosa^H.gourdoni, and Enipo rhomligera) ; (2) 

 Selioides tardus Gravier, from Hermadion rouchi Gravier, closely alHed 

 to S. bolbrsei from a Greenland specimen of Harmothoe imbricata ; (3) 

 Eurysileniopsis sarsi Gravier from Trypanosyllis gigantea^ with some 

 resemblance to Eurysilenium truncatum Sars found on Harmothoe 

 imbricata ; (4) Bactropus cystopomati Gravier in the intestine of a new 

 Serpulid Cystopomatus macintoshi Gravier ; and (5) Zanclopus aniarcticus 

 Gravier, the vermiform females of which were found in the stomach of 

 Gephalodiscus anderssoni Gravier. 



* Zeitschr. wiss. Zool., cii. (1912) pp. 646-700 (2 pis. and 12 figs.). 



t Internat. Rev. Hydrobiol., Biol. Suppl., ser. 3 (1912) pp. 1-10 (5 figs.). 



X Deuxieme Exped. Antarct. Fran^aise, Sci. Natur., 1913, pp. 27-77 (60 figs.). 



