April, 1913. 



KNOWLEDGE. 



147 



of Ailsa Craig, the " ocean pyramid " rising in the middle of 

 the Firth of Clyde, but other types occur at Mynydd Mawr 

 in Wales, in the island of Skye, and in the Lower Carboni- 

 ferous eruptives of the Kildon Hills, near Melrose. A further 

 example, recently discovered by the writer, is important, since 

 it occurs with much the same geological relations, and only a 

 few miles from Ailsa Craig. The rock referred to forms the 

 great so-called " felsite " boss of the Holy Isle, near Lamlash, 

 Arran. This intrusion rises from the sea to over a thousand 

 feet in a steep pyramidal hill, strikingly similar to Ailsa 

 Craig. The rock weathers deeply to a soft, crumbling, 

 yellowish " felsite " ; but on breaking a large block, the 

 interior is found to be composed of a fresh dark-grey rock, 

 which, on sectioning, proves to contain 

 riebeckite. The rest of the rock is built 

 mainly of short stumpy prisms of sanidine, 

 with a few irregular interstitial grains 

 of quartz. The riebeckite forms typical 

 spongy masses, with a characteristic ^A 



pleochroism from indigo-blue to yellowish- flP 

 green. The rock is a riebeckite- 

 orthophyre, and differs from that of Ailsa ' 

 Craig only in its comparative freedom 

 from quartz. 



MICROSCOPY. 



By F.R.M.S. 



QUEKETT MICROSCOPICAL FlGUR 



CLUB.— February 25th, 47th annual 

 general meeting. The presidential address 

 on "The By-Products of Organic Involu- 

 tion," was given by Professor A. Dendy, 

 F.R.S. After referring to well-known 

 cases of by-products in industry, the 

 President thought that nowhere in the 

 animal kingdom is there a more exact 

 analogy than in the familiar rotifer 

 Melicerta which builds for itself a 

 dwelling-place out of its own waste- 

 products. The main part of the address 

 was devoted to a consideration of the 

 evolution of the very many forms of sponge 

 spicules from the primitive ancestral form 

 consisting, in the case of the Tetraxonida, 

 of four rays diverging at equal angles 

 from a common centre. The development 

 of the orthotriaene, dichotriaene, pro- 



triaene, anatriaene, and discotriaene forms Figur 



was then traced. An altogether different 

 line of evolution from the primitive tetract 

 archetype appears to have given rise to the typical oxeote 

 spicules of the monaxonellid division of the Tetraxonida. In 

 the course of evolution the distinction between skeleton 

 spicules (megascleres) and flesh spicules (microscleres) 

 becomes very marked. Both had, doubtless, a common 

 origin, but whereas the megascleres are obviously adapted as 

 the principal skeletal elements and are arranged accordingly 

 in the sponge, the microscleres are scattered at random 

 through the soft ground substance and in the majority of 

 cases it is impossible to assign any value at all to their 

 presence. They are, however, so constant and characteristic 

 that they afford by far the most convenient and reliable data 

 for the classification of the tetraxonid sponges. The President 

 had previously suggested that the various forms were 

 determined by differences in the hereditary constitution of the 

 mother-cell, and in our ignorance we may assume that such 

 differences arise spontaneously in the germ-plasm, and that it 

 is a mere chance whether or not they may prove to be of any 

 value to the organism. Or, again, the differences may be due 

 to the permutations and combinations of ancestral characters 

 which take place in the maturation and fertilisation of the 

 germ-cells, or to the influence of some change of environment 

 upon the germ-plasm. If the characters of sponge-spicules 

 are really of the nature of mutations it should be possible in 



the future to obtain Mendelian results by hybridisation, but 

 we should require to know a great deal more than we do now 

 about the breeding habits and life-history of sponges before 

 we could hope to bring such experiments to a successful 



issue. 



A USEFUL POCKET CASE FOR MICRO-SLIDES — 

 The microscopist often wants to carry in his pocket a dozen 

 or so slides. It is true that small boxes for holding a dozen 

 or a score of slides are on the market. But one may not be 

 able to obtain these at short notice. Again, it is a convenience 

 to have several of these boxes and those with a limited pocket 

 may be glad to spend a hour or two's time rather than so 

 many shillings. 



The two contrivances hereinafter des- 

 cribed merely require some pieces of card 

 or straw board, a fairly sharp knife, some 

 fish glue or strong gum solution, and a 

 little patience, for their making, which is a 

 very simple matter. 



If the reader is not a photographer he is 

 pretty sure to have the acquaintance of 

 one, from whom he can, for the asking, 

 obtain an empty quarter-plate card-box 

 with lid, and very probably also some 

 fairly stout pieces of yellow straw board, 

 such as is often sent out as packing along 

 with packets of bromide and similar 

 E 142. printing papers. The quarter-plate meas- 



ures four and a quarter by three and a 

 quarter inches, and the boxes are about 

 four and a half by three and a half inches 

 inside, and one inch or so deep. 



In Figure 142 we see such a box fitted 



to carry three-inch micro-slips. First 



we cut a number of cards one inch long 



and one-tenth to one-eighth of an inch 



wide. Next cut two strips one inch wide 



and four and a half inches in length, i.e., 



just to fit the inside of the longer side of 



the box. The short bits are fixed to the 



two longer pieces with an interspace just 



large enough to take the thickness of a 



glass slip easily. This, I find, provides for 



sixteen slips in a quarter-plate box. As 



the box is three and a half inches wide, 



and the slips only three inches long, we 



have to pack up with extra strips of card 



e 143. four and a half inches by one inch behind 



each side piece. In my case two pieces of 



packing behind each stepped piece gave an 



easy fit. A glance at Figure 142 will make all clear. The 



triangular object behind the open box containing one mount 



and one clear glass is the box lid on which the box is resting 



to tilt it up for the purpose of being photographed. 



We microscopists frequently want to lay aside a number of 

 freshly-made mounts in a horizontal position to set, or dry. 

 If such a box be set up to rest on its smaller end, we have 

 such a contrivance. Half-a-dozen of these drying boxes (i.e., 

 containing ninety- six slips), tied back to back in pairs with a bit 

 of thread, take up very little room, and can be left on the top 

 shelf of a book-case, thus drying off slides in a few hours. 



The second contrivance is, perhaps, a little more trouble to 

 make, but has the advantage of holding the mounts horizontal 

 when the box is laid flat on the table in the usual way. Here, 

 again, we utilise a quarter-plate box. The complete article is 

 shown in Figure 143 ; the box, is shown containing four card 

 trays, each tray carrying four mounts (Figure 144). A semi- 

 circular piece of card is cut away from the centre of one side 

 of the box (Figure 143), to enable one to lift out the trays. 

 To the inside of the lid are fixed by fish-glue two folded-up 

 strips of thick cloth. These form a kind of soft spring pad, 

 which keeps the contents of the box from shifting about when 

 the box is being carried about in the pocket. 



A glance at Figure 144 shows that either of the two central 



