114 BRITISH APHIDES. 



between the two bodies. The ephippial egg is usually 

 twice the size of the true ovum, and is in effect an 

 aggregation of cells ; in fact, parts, or sometimes the 

 whole of the ovary is encased in a shell with its 

 membranes, so as to simulate true ova. 



To summarise the foregoing remarks ; two varieties 

 of ova may be characterised. The first represents the 

 ovum proper, which is the direct product of the sexual 

 process. The second is altogether non-sexual, and is 

 known by a variety of terms, as statoblast, ephippial 

 egg, pseudovum, winter egg, gemma, bud-germ, or 

 spore. 



All recent research points to the belief that ova are 

 the means finally resorted to by nature for specific 

 maintenance ; and that for reproduction, a conjugation 

 of simple cells of different potentiality is a constant 

 phenomenon. 



In almost the identical words of Dr. Allen Thomson,* 

 ''Multiplication entirely without any known sexes has 

 been remarked in very few instances. In others, the 

 non- sexual process of generation gives rise eventually 

 to sexes which arc simply the repetition of the parent. 

 If a nou-sexual multiplication occurs, it takes place 

 during the incomplete condition of the animal." 



A remark by Prof. E. Kay Lankester may be here 

 added, as it refers to the eggs of the little Ento- 

 mostracan Apus, which " escape from follicles as a 

 matter of course, and pass along the canal leading 

 from it to a primary branch of the ovarian tube, and 

 then two or three eggs fuse into one mass, around 

 which a shell is accreted, and this forms the actual 



egg" 



In Pyrosoma five embryos may come from one egg ; 

 but this is the converse of the foregoing. Prof. 

 Huxley remarks to me thai this is really a process of 

 budding. 



The unimpregnated ovum of the hen, and even of 



* Dr. Allen Thomson, " Ovum," * Todd's Cycl. of Anat.' Sup., pp. 

 33, 37, 137. 



