246 TUE entomologist'cj KECOKU. 



Orders of Hexapoda " ajopear to possess oenocytes in their larval and 

 adult forms. He then goes on to say that the oenocytes are of very 

 general perhaps universal occurrence among the Ptery(jota, Lepidoptera 

 being one of the Orders in which they are found. Of their occurrence 

 in this Order he writes : — " Few insects appear to be better adapted for 

 tracing out the origin of the oenocytes than the Lepidoptera. This is 

 especially true of the larger Bombycid moths. That the segmental 

 cell clusters arise by delamination from the ectoderm was conclusively 

 made out in the embryos of PJatysamia cecropia and Telea polyphemns. 

 Each cluster is several cell-layers in thickness and lies just behind and 

 a little ventral to an abdominal stigma. The succulent cells constituting 

 the cluster are at first polygonal from mutual pressure, but as the time 

 for hatching apj^roaches they become rounder and more loosely united. 

 I have not traced them through the larval stages and merely record 

 these fragmentary observations because they completely confirm Tich- 

 omiroff's and Graber's observation on the origin of the oenocytes from 

 the ectoderm." 



17. — On the origin of the reproductive cells. — The earliest de- 

 velopment of the ovum and spermatozoon in the embryo of insects is 

 very obscure, but it would appear that the primitive ovaries are com- 

 posed of a mass of cells, produced by an infolding of the ectoderm ; but 

 whilst some writers assert that they arise from the ectoderm, others con- 

 sider them to be derived from the mesoderm, whilst still others trace 

 their origin back to certain so-called pole cells, which originate even 

 before the blastoderm is formed. However this may be, it would appear 

 that they are in that early stage quite indistinguishable from the other 

 blastoderm cells. 



Therefore it would ajDpear that whilst the great mass of cells become 

 differentiated into various structures which subserve a special purpose, 

 or perform their several functions, certain cells in the ovary retain their 

 primitive condition, and with it the power, under suitable conditions, of 

 forming another individual of the same species. On this subject Mr. 

 Woodworth writes {loc. cit.) : — "About the time of the completion of the 

 blastoderm, the already differentiated ventral plate infolds at a point on 

 the median line about two-thirds from the upper end, and forms a very 

 narrow pocket. The cells composing it look like the rest of the cells of 

 the ventral plate at this time ; they are almost round, and have a lining 

 on one side made of the grey matter which originally bordered the whole 

 egg, but which became a part of the blastoderm-cells. The pocket re- 

 mains open but a short time, but there is a long depression at the upper 

 end of the bunch of cells ; the mass of cells is soon cut off from the ventral 

 plate and they are then free in the body cavity, but remain in contact 

 with the ventral plate at the point where they were produced. Later 

 stages show that these cells produce the generative organs ; the generative 

 organs thus appear to be produced by an infolding of the ectoderm, or 

 possibly of the blastoderm, before the ectoderm is produced, but from 

 a portion which is later to become ectoderm. The general idea has 

 been that the generative organs in insects are produced from the 

 mesoderm, although Metschnikow, as early as 18G6, showed for certain 

 insects a different origin." 



18. — On the homologies of certain organs and appendages. — 

 There is a remarkable pajier by Mons. N. Cholodkovsky " On the 

 Embryonal Development of FhyUodromia germanka," published in 

 the Mem. de VAcad. de St. Petershourg, 7th series, v., p. 38 (1891), and 



