OVUM. 



1113] 



Fig. 79* 



Development of the ova of Lepidopterous Insects. 

 {From Hermann Meyer.) 



b. A small portion of the upper part of the ova- 

 rian tube from the larva of Saturnia Carpini. The 

 entire lines mark the basement membrane of the 

 tube; externally elongated epithelial cells are 

 placed on it ; internally a number of larger and 

 smaller free nuclei are imbedded in an albuminous 

 fluid. 



a. A similar portion of the ovarian tube from 

 Bombyx Mori more developed. The external epi- 

 thelial cells are visible now only as elongated 

 nuclei; a part of the internal cells now form a 

 lining to the wall of the tube, while others of a larger 

 size, which have become complete cells, towards 

 the centre, form the primitive ova ; of these last 

 only a few undergo farther development. 



c. One of the loculi or chambers of the oviduct 

 of Hyponomeuta variabilis. The wall of the tube 

 with its external epithelial nuclei as before, enclos- 

 ing now the entire loculus and the small portions 

 of the adjacent ones represented in the figure. The 

 lower half of the loculus is occupied by the deve- 



Sujjp. 



loped hemispherical ovum in which the several 

 parts, viz. germinal vesicle with macula, yolk and 

 vitelline membrane, are seen. The lining cells of 

 the oviduct are seen to be elongated and modified 

 in structure preparatory to their forming along with 

 the albumen one of the external coverings of the 

 ovum (chorion). In the middle of the upper half 

 of the loculus there are the remains of five aborted 

 primitive ova. 



d. Section of the coverings of the ovum of Har- 

 pyia vinula, which may be taken as an example of 

 the hemispherical ovum of Lepidopterous insects. 



of the oviduct, there are to be seen in the in- 

 tervals between the ova numbers of large clear 

 globules or cells, which have been supposed 

 to furnish the materials for the growth of the 

 ovum ; but it appears more probable that 

 these are merely abortive ova or germinal 

 vesicles, which, though at first similar in size 

 and structure to those which have been farther 

 developed, have undergone a retrograde pro- 

 cess, and are ultimately removed by absorp- 

 tion. 



The production of the chorion or shell 

 membrane does not take place till the ovum 

 has attained nearly its full size. It appears 

 to proceed in part from the consolidation, 

 over the whole surface, of one or more layers 

 of albuminous fluid secreted from the wall 

 of the oviduct. But the observations of 

 Hermann Meyer * have shown, in an in- 

 teresting manner, that a part of the outer 

 membrane is also derived from a conversion 

 into it of the inner cellular or epithelial lining 

 of the oviduct, at the place where it is in 

 closest contact with the surface of the ovum. 

 Many of the varieties in the appearance and 

 structure of the external covering may pro- 

 bably depend on the different modes of deve- 

 lopment of these cells. As to the origin of 

 the micropyle, it does not appear to proceed, 

 as has been supposed by Meissner, from the 

 mere deficiency of these cells in a certain space; 

 and it is not dependent, either, on its pre-ex- 

 istence in the vitelline membrane. On the 

 contrary, according to Leuckart, it is formed 

 in the chorion before it appears in the vitel- 

 line membrane ; and it is not in any way con- 

 nected with an early pediculated condition of 

 the ovum, which, as is well known, never at 

 any time exists in insects. 



Before leaving the history of the ovum in 

 this class, it may be proper to make the fol- 

 lowing addition to what was stated in an 

 earlier part of the article in reference to the 

 remarkable modification of the reproductive 

 process, by which, in the Aphides and several 

 other insects, many individuals are produced 

 without the formation of true ova, or the con- 

 currence of the two different sexual products. 

 The learned editor of the American transla- 

 tion of Von Siebold's " Comparative Anatomy 

 of the Invertebrate Animals," Dr. Waldo 

 Burnett, has given, at p. 464*. of that work, a 

 short statement of his own observations on 

 the origin and mode of formation of the re- 

 peated broods or colonies of Aphides, made 

 on a large species of that insect, viz., A. 



* Zeitsch. fiir Wissen. Zool., vol. i. p. 190. 



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