100 Transactio ns of the 



hidden from ordinary view, like the concoction of gems in the 

 lower parts of the earth, unvisited by rays from sun or moon. As 

 you may suppose, all the parts in the youngest specimens are very 

 soft ; much of their tissue being a sort of jelly, having little cells, 

 or masses of " bioplasm " scattered through it. When a more solid 

 structure is about to be formed, the cells breed rapidly, and thus 

 clouds of more crowded granules are found gathering together, as 

 the vapours gather together in the sky. In fine sections, that have 

 been stained with carmine, these cell-clouds are extremely beautiful ; 

 perhaps the most elegant object of this sort is the nascent tooth- 

 pulp, which has the appearance of a granular fruit, such as a mul- 

 berry. As for the blood-vessels, streaks of cells are formed, which 

 run into each other, to make a network ; the outer cells form the 

 wall of the vessel, and the inner ones, proliferating rapidly, fill the 

 tube with blood disks, which float free, and circulate at a very early 

 period through the canals. The cartilage is at first merely a cloud 

 of granules, distinguished from the surrounding tissues by their 

 closely-packed condition. They breed at this stage with extreme 

 rapidity. Gradually these masses acquire a clear margin, and then 

 a pith and a bark can be seen in sections ; the pith is cartilage, the 

 bark is its investing perichondrium. And so for tissue after tissue ; 

 for if a cavity has to be formed, the cells vacate a certain region, and 

 then the new-born cells, standing on end, and closely packed together, 

 become its epithelium, or lining skin. The first formation of the 

 cranium is not an easy process to observe. In its simplest part, at the 

 roof, it is merely the innermost part of the skin, subdivided again 

 into a dense membrane, — the dura mater, and the cranial roof bones 

 external to this. But the floor and side-walls are pre-formed in 

 cartilage, the morphology of which it is not easy to make out. All 

 the specimens from which my objects are made, are preserved in 

 alcohol; nothing can take the place of this old-fashioned way of 

 keeping moist tissues. Beginning with the youngest, these, for 

 sections, are dried on blotting-paper, and imbedded in paraffin ; a 

 sharp razor being used for slicing them as they lie in the cheesy 

 mass. The slices are one by one transferred into alcohol again, by 

 the use of a small bent slip of tinfoil ; they are then stained with an 

 ammoniacal solution of carmine, and are mounted in glycerine, to 

 which a small quantity of muriatic acid has been added. The 

 sections thus prepared are very beautiful, the protoplasmic masses 

 taking up the colour very rapidly. As soon as cartilage begins to 

 be formed, the intercellular substance not taking up the colouring 

 matter, a very different appearance is presented, and the tracts of 

 this tissue are well marked. For making solid sections, and for 

 dissection of the early embryos, I prefer to put them for awhile 

 into a weak solution of chromic acid ; they can then be divided 

 vertically or horizontally, being held between the finger and thumb. 

 Dissection must be done in water, on a black substance ; paraffin 



