1890.] [Ryder. 



significance of this fact must also be constantly borne in mind, as well as 

 the equally important one respecting the usual morphological equivalence 

 of myriads of the smaller or male germ cells and a single large or female 

 germ-cell, in the majority of higher forms. 



This frequent, indeed usual, lack of equivalence of the male and female 

 reproductive bodies has been almost entirely ignored by many authors, 

 and has led, as the present writer is convinced, to erroneous interpreta- 

 tions of some of the most important phenomena of subsequent develop- 

 ment. The peculiar function of growth of the female cell and its special- 

 ized method of segmentation, after the initiation of development, has 

 apparently contained little of significance for the great majority of biolo- 

 gists. Segmentation of the oosperm, as the fertilized egg is termed, is a 

 matter of course with the majority of embryologists, whose work begins 

 with the institution of segmentation and not with any apparent anxiety 

 as to the origin or cause of the thing which segments, and which does 

 little else for a considerable space of time. While the high value of the 

 work done through careful embryological research is to be properly 

 appreciated and is so appreciated by no one more than by the present 

 writer, I believe that embryological teaching and investigation should 

 begin with a consideration of the probable causes which have led to the 

 production of the fully developed, and united elements which are usually 

 the subject of the embryologist's study. 



The universal occurrence of sexuality amongst all plants and animals, 

 except amongst the very lowest forms, is surely evidence enough, if any 

 were needed, that somehow sex must have been a most important factor 

 in biological development. To say that sexuality was developed solely 

 for the purpose of inducing variability or of favoring fertility and vigor 

 through crossing does not suffice in the face of the evidence presently to 

 be offered. When the defenders of the view, that sexuality was developed 

 in order to favor variability and cross-fertilization, are asked to give any 

 probable reason for the origin of sexuality, the causes alleged are such as 

 have seemed, to the present writer at least, so unsatisfactory that they are 

 hardly worth serious attention. 



What, then, was the origin and meaning of sexuality? What were 

 some of the causes which may be reasonably supposed to have been oper- 

 ative in inducing sexual differentiation ? Was sexuality differentiated for 

 any purpose, or was its development merely the result of the operation of 

 natural causes ? These are some of the questions that the present writer 

 has set before himself to answer, with such light as may be derived from 

 the facts in the present state of our knowledge. 



The value of this attempt at an approximation to an answer to these 

 questions must be determined by the judgment of those most competent 

 to form an opinion and the value of the results as a working hypothesis 

 in the hands of such persons. 



If, as the writer believes, sexuality has been the means through which 

 morphological complexes or organisms of all sorts, animal and vegetable, 



