HALF-AN-HOUR AT THE MICROSCOPE. 253 



defined margin exists between them and the hair, to which the 

 tubercles adhere as so many scales." The date of this publication 

 is 1850. This statement is repeated in the first volume of 

 " Quekett's Lectures on Histology" (p. 12), and figures given; 

 date of publication 1852. Multiplied observations made with the 

 greatest care show that this is not a correct statement of the facts. 

 In reality, the protuberances are part and parcel of the cell-wall 

 itself, which becomes bulged out here and there — a simple form of 

 " corrugation of surface,'" a principle applied with endless detail in 

 animal and vegetable structures, and often in a very beautiful, 

 interesting, and instructive manner. Sectional views may easily 

 be obtained to substantiate the statements here made. The 

 " fornix " is the throat of the flower ; in this part of the common 

 pansy are hairs showing the structure beautifully ; and in the same 

 part of the garden verbena it is shown still more conclusively 

 because of the larger size of all the parts. I do not think that 

 external deposit on vegetable cell-walls has ever been proved to 

 take place. 



Spine of Amphidotus cordatus (PL XVIII. , Figs, n — 14). — 

 The genus Amphidotus is so closely allied to Spatangus that few 

 authors recognise its distinctness. The structure of the spines in 

 the two appears to be absolutely the same. Sections are required 

 in order to explain the structure. 



Calcareous Plates from Skin of Holothuria (PI. XVI 1 1., 

 I^ig- 15)- — The species from whence these were obtained 

 should have been ascertained and stated. In order to understand 

 what we have before us, a portion of the skin should be shown, 

 with plates, etc., i?i situ ; also, a transverse section. The double 

 columns are homologous with the "anchors" of Synapta ; the 

 plates, formed of a calcareous network, are imbedded in the skin, 

 and serve as '•''points d'appui^^ for the former. They have a strong 

 resemblance to those exhibited by another member, and called 

 " Spines of T/iyone papulosa ; " so strong, in fact, that I suspect 

 their identity. 



Cheyletus eruditus (PL XIX., Figs, i — 5). — This creature 

 preys upon other acari, and, as would be guessed from the power- 

 ful antennal forceps and the lancets forming the oral apparatus, is 

 amongst them like a very tiger, in a flock of defenceless lambs. 

 An extremely interesting description of its structure and habits has 

 been given by Richard Beck, in the 14th Vol., new series, of 

 " Transactions of the Microscopical Society of London." He 

 first found one or two specimens only, which it was desired to 

 keep alive for continuous observation ; ascertaining the proper 

 food, he was enabled to do this without difficulty. The male he 



