McCrady.] 172 [April 18, 



Spencer in his Law of Evolution, with additions, however, which 

 introduce again new confusions of ideas of a lamentable, and at the 

 same time, of a ludicrous character. 



With the history of the subject, as well as with what I have to 

 offer as the approximately correct expression of the Law of Devel- 

 opment, I propose to deal in another work; the present paper is 

 limited to the question whether the course of development in animals 

 is really a progress from the homogeneous, so far as its very earliest 

 steps immediately following the constitution of the new being are 

 concerned. 



It has always appeared to me the most serious difficulty in the way 

 of granting the validity of such a law, that the impregnated egg in 

 animals is really a highly complex bundle, which if not satisfactorily 

 explained, must go far towards the rejection of the idea that the 

 progress is from simple to complex. For if the progress of develop- 

 ment be a gradual passage from the simple and homogeneous to the 

 complex and heterogeneous, then the simplest and most purely 

 homogeneous phasis of every animal's life, should be precisely this 

 earliest one, immediately succeeding the union of the sexual elements, 

 and which I shall call the protembryo, or protembryonic stage. 



I was by these reflections, therefore, led to seek a satisfactory ex- 

 planation of the apparently great and anomalous complexity and 

 heterogeneity of the protembryonic stage, and the following provis- 

 ional theory was the result of my inquiry. 



The essential points of the theory here presented are the following, 



1. That the whole egg is an amoeba-like individual, in which the 

 protoplasm of the yolk represents the ordinary protoplasmic mass of 

 the amoeba; the organic food-particles and granules represent the 

 embedded food of Amoeba; and the germinative vesicle with its con- 

 tents represents the nucleus of an Infusorium or Protozoon. 



2. That the spermatozoon likewise represents a protozoon, gen- 

 erally one of the Flagellata, and its nucleus the male element of the 

 Protozoa. In the spermatozoa of the Nematoids we have Arcella- 

 like forms ; in the motionless spermatozoa of some Crustacea, forms 

 which may be compared to Polycystina. 



3. That the act of generation consists in an actual conjugation of 

 at least two of those protozobids (one ovum and one spermatozoon) : 

 but probably of a plurality of spermatozoa with one ovum in most 



