310 SUMMARY OF CURRENT RESEARCHES RELATING TO 



transformed into " rhomhogens " ; (3) a hermaphrodite generation of 

 " infusorigens," which arise inside the rhomhogens ; (4) an asexual 

 emigrant generation ; and (5) an asexual generation in some host (still 

 unknown) different from the Cephalopod. There is a period com- 

 parable to the Orthonectid's stay in its first host, and there is a period 

 in the kidneys of Cephalopods. The latter has been, as it were, inter- 

 calated between the emergence of the Orthonectid from its first host 

 and its return to the same in the form of an infusiform larva arising 

 from a fertilized ovum. A Dicyemid is a hermaphrodite Orthonectid 

 which, instead of reproducing in the sea, penetrates into the kidneys 

 of Cephalopods, becomes asexual, exhibits several generations, and 

 eventually gives rise to the larvae which find the primary host. 



J. A. T. 



Rotatoria. 



Controlling Sex in Rotifers. — D. D. Whitney {Journ. Exper, 

 ZooL, 1917, 24, 101-138,4 figs., 4 diagrams) finds that when the green- 

 food supply {CMamydomonas) is very abundant the rotifers Brachionus 

 militaris, B. bakeri and Euchlanis cUlatata produce a high percentage of 

 male-producing daughters. If the same food is scanty, very few, if any, 

 male-producing daughters are produced. The same is true for the 

 marine B. midhri for either green or colourless food. A race of New 

 Jersey Hydatina senta fed on Chhmipdomonas in the dark without 

 excess of oxygen present produced male-producing daughters nearly as 

 readily as in the light with an excess of oxygen. The excess of oxygen 

 in the culture water acts indirectly on the mother rotifers by influencingr 

 the number of micro-organisms which form the food. J. A. T. 



Echinoderma. 



Permeability of Sea-urchin Ova, — Ralph S. Lille (Amer. Journ, 

 Physiol., 1918, 45, 406-30) finds that fertilized eggs of Arbacia and 

 Echinarachnius shrink rapidly and undergo creuation in hypertonic 

 sea- water or van't Hoff's solution (of thirty to forty atmospheres osmotic 

 pressure), while unfertilized eggs shrink slowly in the same solutions and 

 remain round. The relative rates of swelling in dilute sea-water are 

 similar. It follows that fertilization results in a marked increase in 

 the permeability of the plasma-membrane (the semi-permeable surface- 

 layer of protoplasm) to water. Artificial formation of fertihzation 

 membranes by butyric acid causes similar though more variable effects 

 in Arbacia eggs. The change in permeability begins two and four 

 minutes after fertilization, and is completed in about twenty minutes. 

 The increase of permeability is prevented by anaesthetics and some other 

 reagents. J. A. T. 



Homologies of Anal Plate in Antedon. — F. A. Bather {A7in. 

 May. Nat. Hist., 1918, 1, series 9, 294-302) discusses the homologies of 

 the plate which appears, migrates, and disappears in the posterior iuter- 

 radius of the larval Antedon, and is what is called the anal plate. It 

 has been regarded as homologous with the plate generally known as 



