AND MORPHOLOGY OF APHIS. 213 



unchanged. One sees such portion of the germ-mass taken into the semitransparent 

 body of the embryo Aphis, like the remnant of the yellv in the chick. I at first thought 

 that it was about to be enclosed within the alimentary canal, but it is not so. As the 

 embryo grows, it assumes the position of the ovarium, and becomes divided into oval 

 masses and enclosed by the filamentary extremities of the eight oviducts. . . ." — Ibid. 

 p. G9-70. 



" It would be needless to multiply the illustrations of tlie essential condition of these 

 phjenomena. That condition is, the retention of certain of the progeny of the primary 

 impregnated gerra-eell, or in other words, of the germ-mass unchanged, in the body of 

 the fii'st individual developed from that germ-mass, with so much of the spermatic 

 force inherited by the retained germ-cells from the parent cell or gei"m-vesicle as 

 suffices to set on foot and maintain the same series of formative actions as those which 

 constituted the indixadual containmg them." — Ibid. p. 72. 



" The physiologist congratulates himself mth justice when he has been able to pass 

 from cause to cause, until he arrives at the union of the spermatozoon with the germinal 

 vesicle as the essential condition of development — a cause ready to operate when 

 favourable circumstances concm-, and without which cause these circmnstances would 

 have no eff'ect. 



" What I have endeavom'ed to do has been to point out the conditions which bring about 

 the presence of the same essential cause in the cases of the development of an embryo 

 from a parent that has not itself been impregnated. The cause is the same in kind, 

 though not in degree, and every successive generation, or series of spontaneous fissions, 

 of the primary impregnated germ-cell, must weaken the spermatic force transmitted to 

 such successive generations of cells. 



"The force is exhausted in proportion to the complexity and living powers of the 

 organism developed from the primary germ-cell and germ-mass." — Ibid. pp. 72, 73. 



These statements are repeated in the recently published second edition of Prof. Owen's 

 Lectiu-es on the Invertebrata. 



The paragraphs I have cited contain two kinds of propositions — assertions with respect 

 to matters of fact, and deductions from those assertions. The former are, according to my 

 observations, incorrect ; and, as I conceive, the latter are unfoimded. 



As regards the first citation, for instance, the contents of the apical chambers of the 

 pseudovaria are no( by any means identical ^^ith those " resulting fi'om the final subdivision 

 of germ-cells retained unchanged," as the most cursory comparison of the two structiu'cs 

 ■htII show. 



In the second citation it is affirmed that the germs are perceptible in the embryo before 

 any organs are formed for their reception. This, again, is an error if my observations are 

 correct. The absence of figm-es, and the too vague and general character of the descrip- 

 tions in Prof. Owen's work, render it very difficult to understand what he really has seen ; 

 but I imagine that he has taken the substance which constitutes the rudiment of the whole 

 pseudovarium, and which becomes diiferentiated partly into pseudova, partly into the walls 

 of the organ, for a mass of germs. What is meant by " those two bodies from which the 



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