ALTERNATE AND EQUIVOCAL EEPKODUCTIOX. 



345 



Fig. 366. 



527. The development of the Medusae is not less instruct- 

 ive. According to the observations of M. Sars, a Norwegian 

 naturalist, the Medusa brings forth living young, which, after 

 having burst the covering of the egg, swim about freely for 

 some time in the body of the mother. When born, these ani- 

 mals have no resemblance whatever to the perfect Medusa. 

 They are little cylindrical bodies (fig. 366, a), much resembling 

 infusoria, and like them covered with minute cilia, by means 

 of which they swim with much activity. 



528. After swimming about freely in the water for some 

 days, the little animal fixes 

 itself by one extremity (fig. 

 366, e). At the opposite ex- 

 tremity a depression is gra- 

 dually formed, the four cor- 

 ners (b, /) become elongated, 

 and by degrees are trans- 

 formed into tentacles (c). 

 These tentacles rapidly mul- 

 tiply, until the whole of the 

 upper margin is covered with 

 them (g). Then transverse wrinkles are seen on the body at 

 regular distances, appearing first above and extending down- 

 wards. These wrinkles, which are at first very slight, grow 

 deeper and deeper, and, at the same time, the" edge of each 

 segment begins to be serrated, so that the animal presents the 

 appearance of a pine cone, surmounted by a tuft of tentacles (h) ; 



bees, only, instead of being performed as an organic function, it is 

 turned into an outward activity, which makes them instinctively watch 

 over the new generation, and nurse and take care of it. It is no longer 

 the body of the nurse, but its own instincts, which become the instrument 

 of the development. This seems to receive confirmation from the fact that 

 the working bees, like the nurses of the plant-lice, are barren females. The 

 attributes of their sex, in both, seem to consist only in their solicitude 

 for the welfare of the new generation, of which they are the natural 

 guardians, but not the parents. The task of bringing forth young is con- 

 fided to other individuals, to the queen among the bees, and to the female 

 of the last generation among the plant-lice. Thus the barrenness of the 

 working bees, which seems an anomaly as long as we consider them 

 complete animals, receives a very natural explanation so soon as we regard 

 them merely as nurses. 



