ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 291 



lie just beneath the peritoneal surface. The material demonstrates that 

 while some fluid may pass between the lining cells of vessels on its way 

 to their lumen, by far the greater part goes through the cytoplasm of 

 the cells themselves. 



INVERTEBRATA. 



Mollusca. 

 y. Gastropoda. 



Mollusca from Elevated Marine Beds of McMurdo Sound.* — 

 €harles Hedley reports on a collection of shells, mostly of small size, 

 collected on Sir Ernest Shackletou's Expedition from elevated marine 

 beds, "raised beaches," of McMurdo Sound. There are twenty-one 

 Oastropods and eight Lamellibranchs, and the Gastropods include 

 three new species, which are described, TurhoniUa ijolaris, Trophon 

 priestleyi, and Return frigida. 



S. Lamellibranchiata. 



Artificial Parthenogenesis in Cumingia.f — Margaret Morris has 

 made a cytological study of artificial parthenogenesis in the mollusc 

 Cumingia teUinoides. The process was induced by exposing the eggs to 

 temperatures ranging from 32-37° C, and then to hypertonic sea-water. 

 The highest percentages of cleavage-stages and swimming larvse are 

 obtained when the eggs are exposed to 32° C. for an hour. The highest 

 percentage of polar body formation is obtained when they are exposed 

 to 37° C. for one and a half minutes. By isolating eggs without polar 

 bodies and observing their development, it was found that they may 

 form fairly normal swimming larvre. Those with polar bodies form 

 non-cellular embryos, if they develop at all. 



Cytological study of eggs which have not formed polar bodies shows 

 that the chromosomes of the first polar spindle divide, and two nuclei 

 are formed which fuse to form a cleavage nucleus. In the cleavage of 

 these eggs there are fifty or sixty small rods of chromatin, instead of 

 the thirty-six threads found in the normal Q^g. Cleavage often follows 

 the normal pattern very closely. The chromosomes of the second polar 

 spindle may also divide and form two nuclei which fuse. Very few of 

 the eggs with one polar body divide. Eggs with two polar bodies may, 

 in rare instances, divide once or twice. Eighteen chromosomes (the 

 haploid number) are found in such eggs. 



Maturation and Development in Cumingia Egg. J — L. V. Heilbrunn 

 describes some experiments in inducing maturation and initiating 

 development artificially in the Q^g of the mollusc Gumingia. The Qgg 

 is immature when shed into the sea, and it remains so unless it is 

 fertilized. Soon after the entrance of the sperm the first polar body is 



* Reports Sci. Invest. Brit. Antarc. Exped. 1907-9, Geology, ii. (1917) pp. 85-S 

 (3 figs.). 



t Journ. Exper. Zool., xxii. (1917) pp. 1-51 (8 pis. and 4. figs.). 

 X Anat. Record, ii. (1917) p. 362. 



