208 PROF. HUXLEY ON THE AGAMIC REPRODUCTION 



the oviduct ; biit as development proceeds, the upper globular chamber becomes by 

 degrees separated by a constriction, and at the same time a great difference makes its 

 appearance between the upper and the lower chambers : for the lower chamber contains 

 a finely granular mass which gradually becomes modelled into an oval egg ; the upper 

 chamber, on the other hand, is filled with vesicular bodies, in which smaller vesicles con- 

 taining a nucleus are distinguishable. If these bodies are to be regarded as germs of 

 ova (Wollte man diese blasenformigen Korper als Eier-keime betrachten), we may assume 

 that these Aphides were capable of bringing forth more than eight ova." 



Von Siebold then goes on to describe the colleterial glands, and the spermatheca, which 

 had not before been seen. If the ovaries of Aphis Lonicerce are not constructed on a totally 

 diiferent plan fi-om those of the species I have described, it is, I think, pretty clear that 

 Von Siebold, like Morren, has mistaken the ovarian glands for the rudiments of the ova. 

 Indeed, his phraseology indicates that he himself had no great confidence in his interpre- 

 tation of the parts. 



§ 4. The Development of the Fseudovarium. 



In the viviparous female, the germ increases in size, and gradually becomes separated 

 from the terminal chamber by the successive development and separation by constriction 

 of new pseudova. The number of chambers between the terminal one and that nearest 

 the vagina, therefore, varies until it attains its maximum, which is necessarily regulated 

 by the ratio between the time requii'ed for the perfection and birth of a larva, and the rate 

 at which new pseudova are detached from the pseudovarium. In the species of Aphis 

 which I examined, I found ordinarily four or five such chambers. Germs between Tooth 

 and -jToth of an inch in length presented the following characters (PI. XXXVII. fig. 1) : — 

 They exhibit a central darkish matter, surrounded by a clear cortex. The latter is com- 

 posed of a single layer of a substance similar in appearance to that composing the mass of 

 the germ above described, while the central substance is obscured by a number of minute 

 graniiles which hide its internal structure. Nevertheless, I have occasionally detected 

 what I believe to be endoplasts, scattered through its substance, as in PI. XXXVII. fig. 1, 

 wliich represents a germ in this stage treated with very dilute acetic acid ; and as in a 

 more advanced condition we shall find such bodies easily recognizable, I do not doubt 

 that the central substance has the same fundamental composition as the peripheral layer. 

 The central mass, it wiU be observed, completely simulates the vitellus of an impregnated 

 ovum ; and I will therefore term it a " pseudovitellus." The peripheral clear layer is, 

 on the other hand, in all essential respects comparable to a blastodermic vesicle ; and I see 

 no reason why it should not be called a blastoderm, since the term is not necessarily con- 

 fined to the product of impregnation. 



In a more advanced condition (fig. 3), the blastoderm has become thicker in all parts, so 

 as to consist of at least two or three layers of " cells ;" but the thickening shows itself 

 especially upon one side of the distal end of the germ (that turned towards the vagina), 

 where the blastoderm is nearly twice as thick as in other parts. A linear demarcation 

 appears in the midst of this thickened layer (fig. 4) ; and at the same time indications of 

 a separation are traceable between the distal extremity of the thickened portion and the 

 rest of the blastoderm : it is as if the latter were giving way at this point. In some 



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