ZOOLOGY AND BOTAXV, MICROSCOPY, ETC. 407 



superabundance of food mateiial, both with rising and falling tempera- 

 ture. The theory that these appendages are produced directly or 

 indirectly by the higher temperature of the water to act as floats in 

 water of greater fluidity and reduced internal friction, is not confirmed, 

 and is considered improbable. 



7. The type forms reappear, it seems, only from the resting eggs. 

 Nearly all the species examined are subject to various individual variations 

 which must be carefully considered before new species are established. 



Centrifuge plankton is that obtained by means of the centrifuge, and 

 consists of excessively minute animal and vegetable organisms which 

 readily pass through the meshes of the finest bolting silk nets, and which 

 form the main food of a large number of Rotifers and other pond animals. 



Echinoderma. 



Cortical Layer in Sea Urchin Eggs.* — A. R. Moore has tried to de- 

 termine whether the " crust " is essentially a definite morphological struc- 

 ture in the egg, or simply a substance or group of substances which may 

 be broken mechanically and thrown into various forms without alter- 

 ing their essential qualities. He studied the properties of fragments of 

 the eggs of Strongylocentrotuspurjyuratus. Breaking the unfertilized eggs 

 does not lead to membrane formation nor to development, but fragments 

 of such eggs upon being fertilized with sperm, or upon being treated 

 with acidulated sea-water, form fertilization membranes, and in the case 

 of fertilization develop into normal larvae. It is, therefore, concluded 

 that the essential nature of the cortical layer of the %gg is unchanged 

 by mechanical fracture, and that the substances which lie at the basis 

 of membrane formation act like chemical substances in being effective 

 without special reference to tlieir original morphological position. 



Process of Regeneration in Linckia.f — C. Richters gives a detailed 

 account of the processes that go on when an arm of this starfish re- 

 grows the missing four. He follows this process as it affects the integu- 

 ment, the food-canal, the mouth, the anus, the water-vascular system, 

 and so on. 



Coelentera. • 



Pedal Cyst of Chrysaora.J — E. Herouard gives an account of the 

 structure and development of the pedal cyst which is sometimes formed 

 beneath the base of the hydra-tuba or scyphopolyp. It represents a 

 particular form of reproduction, quite different from the encystation of 

 an ordinary naked bud. The contents may remain in a state of latent 

 life for three years. It seems difficult to decide whether they should be 

 regarded as statoblasts or as the results of the development of a partheno- 

 genetic egg. In the formation of the cyst, migrant mesogloeal cells play 

 an important part. 



* Univ. California Publications (Physiology) iv. (1912) pp. 89-90. 



t Zeitschr. wiss. ZooL, c. (1912) pp. 116-75 (42 figs.). 



X Arch. Zool. Exper., Notes et Revue, No. 1, pp. xi-xxv (6 figs.). 



