HARDWICKE'S 8C1ENC E-GOSS IP. 



149 



concurrent reproduction, it is one and the sanae 

 organism that exerts both the power of individual 

 multiplication and the faculty of sexual generation ; 

 whereas iu the case of fertile nurse-forms, it is 

 seldom they possess both ; but if the nurse be 

 endowed with the one, its offspring will be endowed 

 with the other." (" The Beginning : its When and 

 its How," pp. 24:2-3.) It sometimes occurs that the 

 nurse acquires the power of sexual generation, also 

 that the species passes through more than one 

 nurse-form, either similar or diverse, before attain- 

 ing the perfect form of the species. In the aphis is 

 found one of the most decided examples of the 

 fertile nurse-form (and one which it is very easy to 

 study), the immature females standing iu that rela- 

 tion to the perfect insect. 



These fertile females, as has been said before, re- 

 produce by internal gemmation, the bud falling into 

 a proper receptacle in the parent's body, and being 

 produced alive, exactly like its parent, except in size ; 

 each female producing horn 50 to 100 young ones. 

 So rapidly do they increase, that it has been calcu- 

 lated that from one individual there might be 

 descended, under favourable circumstances, the 

 enormous number of 4,000 billions in a single 

 summer. 



Were it not for its many enemies, the increase of 

 the aphides would be beyond all bounds ; but for- 

 tunately for us its enemies are very numerous. 

 Birds consume great numbers, but the larvae of the 

 Ladybird, feeding exclusively on the aphides, de- 

 stroys them wholesale, extracting all the soft parts 

 and leaving the empty skins to testify to their 

 enormous appetites. The larva of the beautiful 

 lace- winged fly destroys great numbers, as does also 

 that of the various species of Syrphidse, In July, 

 1S69, we were visited by a great plague of aphides, 

 and all the three species I have named speedily 

 made their appearance also in great numbers. The 

 ladybirds swarmed in countless numbers, and im- 

 mense numbers of their unsightly larvse soon 

 appeared. The rapidity with which these larvae 

 cleared the aphides from a hop-plant in my garden 

 was truly astonishing. The clusters of curious 

 pedunculated eggs produced by the Lace-wing fly 

 were numerous, as were the perfect insects, than 

 which nothing can be imagined more delicate and 

 beautiful or a greater contrast to its larva, which 

 from its voracity has been named the aphis- lion. 



Another foe is a small species of Ichneumon 

 which deposits its eggs in the body of the aphis, 

 the larvae feeding upon its soft parts. The brown 

 and swollen skins of the insects thus infested may 

 frequently be seen, and if placed by themselves in a 

 glass-topped box, the active little ichneumons will 

 soon burst through their prison and reveal the secret 

 of the death of the unfortunate aphides. 



There is another curious chapter hi the history of 

 the aphis which'-is worthy of notice. It is the un- 



fair treatment which it receives at the hands (or 

 antennae) of the ants. Linnaeus calls the aphis the 

 ant's " cow," and the use to which this sagacious 

 little insect subjects it fully justifies the term. The 

 aphides eject from the two tubes before mentioned 

 as situated one on either side of the abdomen, a 

 quantity of saccharine fluid, which is very attractive 

 to the ants, and forms in some cases almost their 

 only food. This fluid may be noticed overspreading 

 the leaves of plants infested by these insects till 

 they have a glazed appearance, and seem to have 

 been washed with honey and water. It is com- 

 monly called "honey-dew," and was long a puzzle 

 as to its origin. Not only do the ants consume the 

 fluid voluntarily ejected by the aphides, but by a 

 peculiar movement of their antennae upon the 

 bodies of their " cows," excite them to an increased 

 supply. This has not inaptly been called " milking," 

 But even this is not all. Kirby and Speuce give a 

 most wonderful account of the way in which some 

 species of ants, particularly the yellow ant {F.flava), 

 convey the aphides to their nests, and keep them 

 there for the supply of their necessities. The yellow 

 ant makes prisoners of a root-feeding species of 

 aphis {A. rddicum), and even carries off its eggs, 

 which are tended with care and placed in situations 

 favourable for their early development, 



I think it will be allowed that whether we con- 

 sider the aphis as a marked example of the wonderful 

 "nurse-form," as described by Steenstrup in his 

 "Alternation of Generations," and one accessible 

 for study to us all ; or whether we confine our 

 attention to its life-history and the singular con- 

 nection between it and the ant, to which it is so 

 serviceable, there is ample scope for observation, 

 and that too of a character, from the delicacy and 

 exactness required in its pursuit, which must of 

 necessity be good training, should it even only 

 extend to verifying the observations of others on 

 this interesting but generally unwelcome littla 

 creature. 



HISTORY OF THE DIATOMACE^. 



{Concluded^ 



-pROFESSOR H.L. SMITH has published his se- 

 -'- cond instalment of his translation of the " His- 

 torical Preface of Kiif zing." This is for the most part 

 a record of Kiitzing's own labours. In his " Synopsis 

 Diatomearum " he separates the true Diatomaceae, 

 with hard and glassy shells (valves), from the softer- 

 shelled forms, which he called Desmidieae. This 

 seems to have caused some complaints, of a desire 

 on the part of the author to unduly multiply 

 species; but he remarks that "not only all the species 

 established by myself stood proof, but even many 

 a form mentioned by me as a variety, was established 

 by others as distinct species." 



