ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 187 



for the reception of Seligo's Tubicolaria (Conochilus) natans and Gono- 

 chilm dossuarius of Hudson. 



Echinoderma. 



Study of the Nucleolus in the Maturing Ovum.* — K. Guenther 

 has made a detailed study of the history of the nucleolus in Holothuria 

 tubulosa and Psammechinus microtuberculatus. It arises in the ripening 

 ovum as a drop or as several drops excreted from the nuclear frame- 

 work. Into this or these the chromatin of the nucleoplasm penetrates 

 intimately. After a time the chromatin emerges and is re-distributed 

 in the nuclear framework, or it postpones its emergence until the forma- 

 tion of the directive spindle where it takes the form of chromosomes. 

 In both cases there is a residue (Hacker's " metamicleolus "), which is 

 either a product of metabolism or superfluous chromatin. This residue 

 may be immediately dissolved, or it may persist for a considerable time. 

 In short, " the nucleolus represents a drop excreted from the nuclear 

 framework ; into it the chromatin penetrates, and prepares for division. 

 There may be an intense metabolism involved between the chromatin 

 and the nucleolar fluid." 



Development of Echinus miliaris.t — Hjalmar Th^el gives a pre- 

 liminary account of this, dealing in particular with the water-vascular 

 system and with Aristotle's lantern, but including many figures relevant 

 to other parts of the body. 



Sea-Urchin Ova Fertilised by Starfish Spermatozoa.^ — Jacques 

 Loeb finds that in certain solutions, not described, the ova of Strongylo- 

 centrotus purpuratus can be fertilised with the sperm of Asterias ochracea, 

 though this hybridisation will not occur in ordinary sea water. About 

 half of the ova, thus cross-fertilised, developed to some extent, and 

 some formed not only blastulae and gastrula?, but lived for more than 

 a week, and showed a differentiation of the gut, but at most a rudi- 

 mentary larval skeleton. 



Ova of Sea-Urchins.§ — A. Krassuskaja and E. Landau find that 

 the space between the vitelline membrane and the surface of the ovum 

 is occupied by a delicate gelatinous substance, secreted after fertilisation, 

 which absorbs water and swells up so as to remove the vitelline mem- 

 brane from the ovum. 



Parthenogenesis induced by Carbon Dioxide. || — Yves Delage has 

 shown that the ova of starfishes will develop parthenogenetically if sub- 

 mitted to the influence of carbon dioxide during the formation of the 

 polar bodies. The ova of sea-urchins (Paracentrotus = Strongylo- 

 centrotus) give off their polar bodies in the ovary, and are not sus- 

 ceptible normally to the influence of carbon dioxide as a stimulus to 

 parthenogenesis. But it is possible to make them so susceptible by 



* Zool. Jahrb., xix. (1903) pp. 1-2S (1 pi."). 



t Bihang. k. Svensk. Vet.-Akad.-Handl., xxviii. (1903) Afd. iv. No. 7, 9 pp. and 

 3 pis. 



% Univ. California Publications (Physiology), i. (1903) pp. 1-3. See Zool. Cen- 

 tralb)., x. (1903) p. 885. § Biol. Centralbl., xxiii. (1903) pp. 613-8. 



|| Comptea Rendue, oxxxvii. (1903) pp. 473-5. 



O 2 



