Published online by Cambridge University Press: 06 April 2009
The egg of Ixodes ricinus L. is described, and the increase in size during development is noted. It is suggested that the increase is due to the absorption of water. The egg wall consists of exo- and endochorion with a thin vitelline membrane, which becomes thicker as development proceeds and assumes a laminated appearance. The secretion layer of Gené's organ is described, and appears to function as a cement for holding the eggs together in the cluster. Chemical tests show it to be of a waxy nature.
It is deduced from experimental evidence that the egg shell is not absolutely rigid, and the weight of evidence favours the view that the shape of the egg shell is maintained by the internal pressure of the egg contents, and the elasticity of the shell.
The development processes as seen in the living egg are described. Hatching from the egg shell is brought about by a muscular force acting on a limited area at the posterior pole of the egg.
The writer is indebted to Mr Robert David, of Longlands Farm, Pyle, Dr A. D. Lees, of the Agricultural Research Council, and Mr Simeon, of the Glamorgan War Agricultural Executive Committee, for supplies of material; to Mr T. W. Tyssul Jones, M.Sc., for his assistance in checking the measurements of the egg dimensions, and to Mr L. Cowley, M.Sc., Assistant Curator (Department of Zoology), National Museum of Wales, and Dr P. Tate, Molteno Institute of Parasitology, Cambridge, for reading the original script and for making many useful suggestions and modifications.