HARDWICKE'S SCIENCE-GOSSIP. 



53 



what resemble the mealy bug to which they are near 

 relatives. In spite of the fact that later in life they 

 :are very inactive, at this early period they walk 

 freely about and thus it is that the scales are found 

 at sonie distance from each other. Very soon the 

 young coccus settles down and begins to degenerate. 



By very little care you may find scales no larger 

 than these young. At this stage, they are slightly 

 red in colour, and preserve more the appearance of 

 the young than they do later : the eyes are still 

 distinct ; the segments are more clearly marked off from 

 ■one another, the caudal appendages are still present, 

 and the general shape of the body is only slightly 

 convex. As the scale gets older, it becomes larger, 

 anore convex and more scale-like. Sometimes the 

 Tjack is marked with a few black lines which give it a 

 somewhat tortoiseshell appearance. It is at first 

 yellowish-green, then as the markings get stronger it 

 turns brown. Even at this late stage, traces of its 

 former condition may be seen. Thus you usually 

 find at the posterior end a well-marked indentation, 

 and this marks the interval between the two projecting 

 angles of the last segment near the root of the caudal 

 appendages. The eyes, which are very indistinct, 

 and the useless legs and antennc'c can still be seen. 

 The body is very thin, except — if the specimen be not 

 too old — near the middle line where it is sac-like, and 

 contains the young in an embryonic condition. 



In short, the scale is now a degenerate organism, 

 motionless, feeding, increasing in bulk so that it may 

 develop young, and form a shield over them for 

 their protection. The useless organs — that is the 

 ■organs not concerned in this task — have shrivelled 

 away, and the structure has modified itsell to suit 

 this purpose. 



This is a very interesting object for microscopic 

 study, and may be easily possessed by those who 

 have access to a green-house. Besides the species 

 here described, there are others common in green- 

 houses which attack different plants. 



Bernard Thomas. 



ON SOME ADDITIONAL ACCESSORIES TO 

 THE MICROSCOPE. 



By Thomas H. Holland, A.N.S.S. 



IN an examination by reflected light of such ob- 

 jects as sand-grains and small crystals, it is 

 -desirable, sometimes, to investigate the characters of 

 ■surface-markings, such as etch-figures, oscillatory 

 combinations of two distinct crystalline forms, or 

 other external peculiarities of minerals. Again, the 

 great numbers in which the remains of small and low 

 forms of life are found in the fossil state, adds to 

 the importance of their accurate determination by 

 the palaeontologist. In studying specimens of, say, 

 foraminifera, bryozoa, or small brachiopoda, it is 

 necessary to turn the individual about in all sorts of 



manners to examine the appearances presented on all 

 sides. 



Now, one of the chief difficulties in dealing with 

 such small specimens, whether of minerals or of fossils, 

 is to find a convenient method of handling the object, 

 whilst subjecting it to a microscopic examination. 

 In holding the object in the hand, from the way in 

 which one's hand persists in going in the wrong 

 direction when one's attention is occupied with the 

 specimen, it is more a test of patience than a process 

 attended with satisfactory results. The absurdly 

 simple contrivance described below, may, to a large 

 extent, obviate this difficulty. 



A sphere of wood, ivory, cork, or other suitable 



vA\ \'\\\\'v\\'\ "\\\\\\\\\\V \ 



Fig. 23. 



material of about \ in. diameter, is divided into two 

 along the plane of a great circle. Each half is 

 available for use, and out of each, a concentric 

 hollow hemisphere, of less than f in, diameter, is 



Fig. 29. 



turned as shown in Fig. 29. By using a small piece of 

 wax, the specimen to be examined may be so mounted 

 that it is, as nearly as possible, coincident with the 

 centre of the hemisphere, which can be placed, 

 as shown in Fig. 28, over the central circular 

 aperture of the microscope-stage. Seeing the edge 

 of this hole touches the hemisphere in a circle of 

 co'nstant diameter, equal circular sections of the 

 sphere are always cut off, no matter to what angle 

 the plane of the great circle of the hemisphere be 

 tilted. The circle, therefore, is always the same 

 distance from the centre of the sphere, consequently, 

 any object, mounted centrally, always remains at the 

 [Continued on page 56.) 



