794 LIFE : OUTLINES OF GENERAL BIOLOGY 



Antennata), is a widespread type called Peripatus, which, with 

 other nearly related genera, is included in the class Onychophora 

 or Claw-bearers. This relic of an ancient fauna holds its own partly 

 because of its shy elusive habits, hiding under bark, in rotting 

 wood, and among moss; and partly because of its unique way of 

 feeding, for it squirts jets of gluey slime on small insects that pass 

 by; but also because it is viviparous. The young one is nurtured 

 for a long time within the mother — for thirteen months in the Cape 

 species — and it is born fully formed, a miniature of its parents, 

 more or less able to fend for itself. This is the reward of viviparity. 



Unfortunately for Farming and Gardening, great success, as 

 regards material well-being and increase in numbers, has attended 

 the pests known as Aphids, Greenflies, or Plant-lice; and it is 

 not a coincidence that throughout the summer months these 

 theoretically fascinating, but practically detestable, insects are 

 viviparous. In the summer months there are no males, and the 

 parthenogenetic females produce their offspring viviparously. 

 What leaves the virgin mother is an almost perfect greenfly, able 

 at once to suck the sugary juices of plants; and in the course of a 

 week or so this viviparously-produced daughter-Aphis is able to 

 continue the prolific succession. Agriculturally speaking, we wish 

 this viviparity did not exist, but there it is! 



We must not linger in this side-alley of our main theme, but the 

 point is that over and over again in the course of organic evolution 

 a trend towards viviparity has found expression. It must suffice 

 to notice that the outcome of this recurrent trend is illustrated in 

 various orders of insects; in a few fishes, amphibians, and reptiles; 

 and that it becomes the rule in Mammals. 



More Than Viviparity.— In two of the viviparous sharks and in 

 several viviparous lizards there are interesting anticipations of the 

 placenta, which is so distinctly characteristic of ordinary Mammals. 

 That is to say, at the low level of these two fishes, as Aristotle 

 pointed out more than two thousand years ago, a nutritive con- 

 nection has been established between the unborn offspring and the 

 wall of the mother's oviduct. It is also of interest to remember that 

 the seeds of Flowering Plants, as distinguished from the spores of 

 Flowerless Plants, are well-equipped offspring which have developed 

 for a considerable time in nutritive dependence on the parent plant, 

 within which they are hidden away. The comparison must not be 

 pressed, yet it is more than a coincidence that botanists should 

 speak of the placentation of the ovules within the ovary. 



Oviparous and Marsupial Mammals. — When some wide- 

 awake natives of Australia first told the exploring zoologists 

 that the Duckmole laid eggs, the report was received w4th natural 

 incredulity. A mammal could not possibly lay eggs. But the natives 

 were right and the textbooks were wrong: there are two types of 



