188 CARNEGIE INSTITUTION OF WASHINGTON. 



mollusks, paying attention to their development, function, and reac- 

 tions. He concludes that the large apyrene male sex-cells, which, when 

 mature, lack nuclei, probably serve as nurse-cells for the small, active, 

 true spermatozoa or eupyrene sperm of the mollusk. The reactions of 

 one sort of sperm-cells are commonly the opposite of the others. 



Professor Charles R. Stockard concludes that regenerating tissue 

 resembles cancer in that it consumes the old body-substance and has 

 an effect which would finally so weaken the body as to cause death 

 should the regeneration continue for a sufficient time. 



Dr. Frank A. Stromsten finds that in the embryo loggerhead turtle 

 the mesenchymal spaces capture certain capillaries and convert them 

 into the anlagen of the lymph hearts. 



Professor David H. Tennent has ably pursued his studies of the 

 characters of hybrid echinoderm larvae at Tortugas, Jamaica, and 

 Torres Straits, Australia. At Tortugas he showed that in natural sea- 

 water reciprocal crosses between the two echini Hipponoe and Toxo- 

 pneustes give a hybrid larva in which the Hipponoe characters are 

 dominant, and this is also the case if the alkalinity of sea-water is in- 

 creased by the addition of caustic soda. If, however, the alkalinity of 

 the normal sea-water is reduced by the addition of hydrochloric or 

 acetic acid, the hybrid larvae resemble Toxopneustes. Thus Professor 

 Tennent can, at will, cause the hybrid larvae to resemble either their 

 paternal or maternal parents, and has thus, in a sense, been able to 

 artificially control dominance. 



In another research at Montego Bay, Jamaica, Professor Tennent 

 showed that when the Cidaris egg was fertilized with Toxopneustes 

 sperm, the sperm-cell had a decided directive influence upon the rate 

 and mode of development of the larva from the early segmentation 

 stages onward; and while in Torres Straits, Australia, Professor 

 Tennent discovered even more favorable material for a continuance 

 of these studies, and he also succeeded in effecting a cross between a 

 female crinoid and a male echinus, and in carrying the larvae to a 

 later stage than had hitherto been done. 



The important studies of Dr. Thomas Wayland Vaughan upon the 

 geology of limestone regions and the biology, growth-rate, oecology, 

 and physiology of coral reefs has been in part reviewed elsewhere in 

 this report. It will be unnecessary, therefore, to refer again to his 

 studies demonstrating the manner in which the precipitated aragonite 

 ooze of the Florida-Bahama region changes into oolites, nor to his con- 

 tention which confirmed the previous work of Dall, 1892, and Sanford, 

 1910, that this calcareous ooze was a chemical precipitate, a deduction 

 which has been fully confirmed by the studies of Drew and of Keller- 

 man, who have demonstrated that this precipitation of calcium car- 

 bonate is due to the action of several sorts of bacteria. 



Andrews showed that the submerged platform upon the seaward 

 edge of which the Great Barrier Reef of Australia has grown and 



