ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 311 



Structure and Development of Distomum cirrigerum.* — E. Warren 

 gives an account of this parasite, which appears to have a secondarily 

 acquired monogenetic life-history. The sexual form can develop from 

 the egg within the crayfish host, and a cercaria-cyst stage occurs, 

 generally before any cell differentiation has taken place in the embryo. 

 After the blastomeres have divided into quite small cells it seems to be 

 a matter of indifference how many of them are enclosed in the thick 

 cercaria-cyst ; the excluded cells perish, the enclosed mass will develop 

 into the embryo. Hence up to this period there is no sorting out of 

 hereditary tendencies (except that sometimes the primordium of the 

 cirrus-sac appears quite early) into separate cells, but they reside in the 

 mass as a whole. The author is inclined to minimise the importance of 

 the cell as a unit. There are points, too, in the development which 

 tend to weaken the morphological significance of the usual conception 

 of germ layers. 



Incertse Sedis. 



Pelmatosphaera.f — Maurice Caullery and Felix Mesnil describe a 

 new organism — which they call Pchnato splicer a polycirri — found as a 

 parasite in the body-cavity of an Annelid, Polycirrus Jmmatodcs Clap. 

 It is a spherical, abundantly ciliated organism, apparently allied to 

 Orthonectids, giving rise by endogenous multiplication to asexual 

 progeny. 



Echinodernia. 



Fertilisation and Parthenogenesis in Echinoderms.f — A. Sehuek- 

 ing has made many experiments bearing on the physiology of fertilisa- 

 tion and development in Asterias glacialis, Stromjijlocentrotus lividus, 

 Arbacia pustidosa. The mass of ova, with an acid reaction (due to 

 phosphates of potassium and sodium), exerts a fatal, or a paralysing, or 

 an agglutinating, or an exciting and attractive effect on the spermatozoa, 

 according to its amount and duration of influence. The head of the 

 spermatozoon serves for attachment to the ovum, not for boring into it. 

 The spermatozoon is drawn in by a hyaline protuberance of the ovum- 

 protoplasm. The essential event is the union of the two cytoplasms, 

 which seems to be abetted by the centrosomes at the apex of the sperm. 

 In fertilisation an interlamellar splitting of the vitelline membrane 

 allows water to enter, and development then begins. 



Schucking was able to induce parthenogenetic development to an 

 abnormal (delaminate) gastrula stage by the most diverse stimuli,— 

 chemical, thermal, electrical, and luminous. The paper is full of 

 interesting experimental data. 



New Genus of Spatangoids.§ — F. Jeffrey Bell describes a new 

 genus, Eobrissus, of Prymnodesmid 8patangoids, with apex almost 

 central and the anterior ambulacrum flush with the test ; the antero- 



* Quart. Journ. Micr. Soc, xlvii. (1903) pp. 273-301 (3 pis.), 

 t Comptes Retidus, exxxviii. (1904) pp. 217-9. 



•J Piiiigers Archiv. Ges. Physiol., xcvii. (1903) pp. 58-97 (1 pi.). See Zool. Cen- 

 tralbl., xi. (1904) pp. 161-2. 



§ Ann. Nat. Hist., xiii. (1904) pp. 230-7. 



