ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 501 



cup and the zocecia are all situated on the convex surface. In this as 

 well as in detailed structure the new species is very distinct. 



Echinoderma. 



Experimental Studies on Eggs of Echinus microtuberculatus.* — 

 N. M. Stevens divided the ova in an anaphase of the first cleavage into 

 portions containing fewer than the normal number (18) of chromosomes. 

 A portion with a centrosome and 4-12 chromosomes may divide five or 

 i six times without a restoration of the normal number. This is against 

 the conclusion reached by Delage. 



Chromosomes may divide repeatedly without spindle formation or 

 the like. Centrosomes may appear de novo in a blastomere. Pieces of 

 ovum without indication of the first cleavage plane do not exhibit cell- 

 division unless chromosomes and centrosomes are present. 



Experiments on Ova of Starfish. f — Jacques Loeb has made some 

 interesting observations on the ova of Aster ias forbesii. Mature, unfer- 

 tilised ova soon die a natural death in sterilised sea-water, but immature 

 ova, or those whose maturation has been artificially delayed, or fertilised 

 ova live on for a longer or shorter time. Oxygen and free hydroxyl 

 ions hasten maturation, while scarcity of oxygen inhibits it. In 

 naturally parthenogenetic ova there may be a katalytic substance formed 

 inside the cell, while in eggs which require fertilisation it may have to 

 come from without. The treatment with acids that induces artificial 

 parthenogenesis usually inhibits maturation. Loeb supposes katalytic 

 substances which promote synthetic processes in development, and dis- 

 ruptive autolytic processes in maturation. 



Ccelentera. 



Development of Gonionemai murbachii. ! — H. F. Perkins has 

 studied the development of this species which made a sudden appearance 

 in 1894 in the "eel-pond" at Woods Hole, Mass. His observations 

 show that Haeckel's sharp distinction between Trachoniedusge and 

 Leptomedusas is not justified. 



Dehiscence of sex-cells occurs in Gonionema with precise periodicity, 

 and is definitely affected by changes in light. Segmentation is total 

 and equal ; the endoderm is formed by delamination of the blastomeres ; 

 a solid morula results. A planula stage is followed by a hydrula stage, 

 and during the latter four tentacles are developed. 



Youngest medusas and oldest polyps show marked homologies ; and 

 direct metamorphosis is suggested. Peculiar pathological phenomena 

 occur, the larva living for weeks in the form of a plasmodium, with 

 amcebiforni activities. 



Alternation of generations occurs. A non-sexual form of multi- 

 plication takes place during larval life. Buds are produced which are 

 detached as planulae and go through the same changes as the parent. 



The order and arrangement of tentacles in a gonosome follows a 



* Arch. Entwickmech., xv. (1902) pp. 421-8 (1 pi.). See Zool. Centralbl., x. 

 (1903) pp. 416-7. 



t Pfluger's Arch. Ges. Physiol., xciii. (1902) pp. 59-76. See Zool. Centralbl., x. 

 (1903) pp. 379-80. 



X Proc. Acad. Nat. Sci. Philadelphia, liv. (1903) pp. 750-90 (4 pis. and 21 figs.) 



