Animal life and intelligence . ;while in some kinds of rotifers fertilization is said neverto occur. It is a curious and interesting fact, which seemsnow to be established beyond question, that drone bees aredeveloped from unfertilized ova, the fertilized ova pro-ducing either queens or workers, according to the nature ofthe food with which the grubs are supplied. Where, as inthe case of aphids and daphnids, fertilization occasionallytakes place, it would seem that lowered temperature anddiminished food-supply are the determining , therefore, generally takes place in th
Animal life and intelligence . ;while in some kinds of rotifers fertilization is said neverto occur. It is a curious and interesting fact, which seemsnow to be established beyond question, that drone bees aredeveloped from unfertilized ova, the fertilized ova pro-ducing either queens or workers, according to the nature ofthe food with which the grubs are supplied. Where, as inthe case of aphids and daphnids, fertilization occasionallytakes place, it would seem that lowered temperature anddiminished food-supply are the determining , therefore, generally takes place in theautumn ; the fertilized ovum living on in a quiescent stateduring the winter, and developing with the warmth of thesucceeding spring. In the artificial summer of a green-house, reproduction may continue for three or four yearswithout the occurrence of any fertilization. Mention may here be made of some peculiarly modifiedmodes of reproduction among the metazoa. The aureliais a well-known and tolerably common jelly-fish. These. Fig. 9.—Aurelia: Life-cycle. a, embryo; b, Hydra tuba; c, Hydra tuba, with medusoid segments; d, medusa separatedto lead free existence. produce ova, which are duly fertilized by sperms from adifferent individual. A minute, free-swimming embryodevelops from the ovum, which settles down and becomesa little polyp-like organism, the Hydra tuba. As growthproceeds, this divides or segments into a number of se-parable, but at first connected, parts. As these attain theirfull development, first one and then another is detachedfrom the free end, floats off, and becomes a medusoid 46 Animal Life and Intelligence. aurelia. Thus the fertilized ovum of aurelia develops, notinto one, but into a number of medusae,* passing throughthe Hydra tuba condition as an intermediate stage. Many of the hydroid zoophytes, forming colonies ofhydra-like organisms, give rise in the warm months tomedusoid jelly-fish, capable of producing ova and takes place; an
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