52 



HARDWICKE'S SCIENCE-GOSSIP. 



Roman Wall may be seen. We have had but a peep, 

 and that peep has made us anxious to see more. If 

 we cannot satisfy our desires we may procure the 

 veteran Dr. Bruce's work on this subject and study 

 it at our leisure. Now let us away for a wash and a 

 cup of tea to refresh us after our ramble. 



A CHAPTER ON DEGENERATION. 



THERE are certain animals which, beginning life 

 well, gradually lose their characters, become 

 parasitic, or attached to some object, their senses 

 become aborted, their limbs useless, and only the 

 functions of digestion and reproduction are performed 

 with their primary vigour. 



Green-house plants are often troubled with a 

 little pest called the Scale. It is found as a small 

 brown or yellow scale on the leaves and stems of 



divided into segments, each segment bearing a short 

 blunt process on each side. The eyes are small, and 

 situated on each side of the flat round head. It has 

 short, somewhat hairy antennae, and six short legs. 

 Two straight blunt appendages project from the 

 hinder end of the body. In most of these points, as 

 will be seen later, the mealy bug resembles the 

 young of the scale, but it is much fatter, rounder and. 

 covered with meal. If it is disturbed, it may take 

 a step or two, but its nature is very slugg ish, and it 

 seems quite contented to remain in one spot, busily 

 fattening itself. Both the mealy bug and the scale, 

 are female cocci, the males of which are furnished 

 with wings. 



The particular scale which I examined, attacks the 

 Abulilon trees in our green-house, and both it and 

 the mealy bug do considerable damage. It is a small 

 oval, yellow or brown in colour, and varies in length- 

 from one-sixth of an inch _ to a size barely visible ta 



Fig. 15. — Scale on Leaf. 



Fig. 26. — (A; Inside of Scale, showing 

 Young. 



Fig. 27. — (b) Young, much, 

 magnified. 



plants ; sometimes in great quantities, and, as jt 

 spreads (juickly, frequently causes considerable 

 damage. If an old brown scale be lifted from the 

 surface of the plant, minute red bodies, just visible to 

 the unaided eye, are found underneath it. These 

 are the young, while the scale which protects them 

 is a degenerated female insect which lives upon the 

 sap of the plant, and reproduces its young in this 

 manner. The scale insect, then, is a good example 

 of degeneration. 



The mealy bug, which attacks green-house plants 

 in the same manner, is closely related to the scale, 

 although it does not undergo so complete a degenera- 

 tion. It is about the same size (about one-sixth of an 

 inch), and has very much the same manner, of life. It 

 is round in shape, of a reddish colour, and covered all 

 over with a white mealy substance. Its body is 



the naked eye. It is best examined by opaque light 

 with 1-3 in. objective, either on the leaf or on a 

 slide. The young are seen by taking an old scale of 

 the leaf and laying it, lower surface upwards, on a 

 slide. It will then be seen that the scale is more 

 hollowed out in one part where it is black or dark in 

 colour, and that here four or five young cocci are 

 ensconced. They usually present very obvious signs 

 of vitality, and walk all over their shield, evidently 

 unaccustomed to the light of day suddenly brought 

 to bear on them. Their bodies are oval in shape and 

 very flat, with two bright eyes and two long hair-like 

 curved caudal appendages. They have six legs, and 

 two hairy antenna;, which are used as feelers, when 

 they walk about. Their body is divided into several 

 narrow segments, which are elevated into a slight 

 ridge in the middle line. In appearance they some- 



