20 FERTILIZATION 



a few minutes after, fertilization. The same occurs when the 

 eggs of Saccoglossus kowalewskyi and Thalassema neptiini Gaertner 

 are fertiHzed (Colwin & Colwin, 1953; Hobson, 1928). Changes in 

 the shape of the eggs of Ascidiella aspersa after fertihzation are 

 shown in Fig. 6. Rounding up after fertihzation is not due to the 

 influx of water, but to changes in the physical properties of the 

 cortex. These are discussed in a later chapter. 



According to Glaser (1913, 1914, 1924), there is an 8% reduction 

 in the volume of Arbacia eggs at fertilization, but this has been 

 denied by R. Chambers (1921). An 8% change in volume would 

 not be easy to establish with any certainty by measurement of egg 

 diameters; but I do not believe that any reduction occurs in the 

 eggs of Echinus esculentus Linn, or Psammechinus miliaris. A re- 

 duction in volume definitely occurs at fertilization in the eggs of 

 the brook lamprey, of Ascaris equorum Goeze (Faure-Fremiet, 

 19 1 3), of Hydroides norvegicus Gunnerus (Monroy, 1954), of 

 Chaetopterus variopedatus (Monroy, 1954), and of a number of 

 mammals (Pincus, 1936). 



