222 THE INDUCT10^^S OF BIOLOGY. 



specialized, but rather that they are iinspecialized : such 

 Bpecializations as some of them exhibit in the shape of loco* 

 motive appliances, &c., being interpretable not as intrinsic, 

 but as extrinsic^ modifications, that have reference to nothing 

 beyond certain mechanical requirements. Sundry 



facts tend likewise to show, that there does not exist the pro- 

 found distinction which we are apt to assume, between the 

 male and female reproductive elements. In the common 

 polype, sperm-cells and germ-cells are developed in the same 

 layer of indifferent tissue ; and in Tethya, one of the sponges, 

 Prof. Huxley has observed that they occur mingled together 

 in the general parenchyma. The pollen-grains and embryo- 

 cells of plants, arise in adjacent parts of the cambium-layer ; 

 and from a description of a monstrosity in the Passion-flower, 

 recently given by Mr Salter to the Linneean Society, it ap- 

 pears, both that ovules may, in their general structure, 

 graduate into anthers, and that they may produce pollen in 

 their interiors. All which evidence is in perfect harmony 

 with the foregoing conclusion ; since, if sperm-cells and 

 germ- cells have natures not essentially unlike those of un- 

 specialized cells in general, their natures cannot be essen- 

 tially unlike each other. 



The next general fact to be noted, is, that these cells 

 whose union constitutes the essential act of gamogenesis, are 

 cells in which the developmental changes have come to a 

 close — cells which, however favourably circumstanced in 

 respect of nutrition, are incapable of further evolution. 

 Though they are not, as many cells are, unfitted for growth 

 and metamorphosis by being highlj^ specialized; yet they 

 have lost the power of growth and metamorphosis. They 

 have severally reached a state of equilibrium. And while 

 the internal balance of forces prevents a continuance of con- 

 structive changes, it is readily overthrown by externa] 

 destructive forces. For it uniformly happens that sperm- 

 cells and germ-cells which are not brought in contact, disap- 

 pear. In a plant, the embryo- cell, if not fertilized, is 



