HAR D WI CKE ' S S CIE NCE - G O SSIP. 



137 



ago, the former idea was the most prevalent, and I 

 remember the late Richard Beck teaching me the 

 right way to show a Pleurosigma as a pearly shell 

 dotted over with dark pits or depressions ; but now 

 it is the fashion to exhibit them as transparent 

 silicious valves with bead-like elevations. For many 

 years I have been of opinion that both the 

 exterior surfaces of the valves are perfectly smooth, 

 and devoid of markings of any kind ; but that they 

 are composed of two layers or laminje, on the interior 

 surface of one of which are attached a more or less 

 net-like arrangement of ribs, like those on the under 

 side of a Victoria regia lily-leaf ; and that these, 

 resting on the inner surface of the other lamince, 

 form, as it were, so many interspaces, through which 

 the light being thrown at different angles, produces 

 varying effects. I do not remember who suggested 

 this theory ; but I was led to the conclusion by 

 observing that, after having focussed the surface of 

 the valve as exactly as possible, I had invariably to 

 focus downwards before the markings appeared. I 

 need scarcely remark that in the valves of arachnoid- 

 iscus, and of many of the Coscinodisci, there are 

 evidently two distinct lamina, and, from iinalogy, we 

 may presume it may be the case also in other genera, 

 though they are not so easily separable. I have 

 brought forward the subject again, as the other night 

 I was showing to an intelligent relative, but a novice 

 at the microscope, the strong crossed markings on the 

 very coarse navicula rhomboides of the cherry- field 

 deposit. He saw them distinctly, but playing with 

 the fine adjustment to improve them, he exclaimed, 

 " There they are, much better, more like beads ! but 

 irregularly scattered over the shell ! " On looking 

 through the instrument, I found he had focussed up 

 to the surface of the valve, which happened to be an 

 abnormally abraded one, and he had taken these 

 abrasions for the beads. He had afterwards to 

 focus considerably downwards, so much so, that the 

 superficial abrasions were lost sight of, before he 

 could recover these markings. Q.E.D. as we used to 

 say in Euclid. — Fred. H. Lang. 



A New Microtome.— Mr. A. B. Chapman has 

 just registered a very ingeniously constructed Micro- 

 tome, which has for its cutting surface two parallel 

 glass plates cemented to a block of mahogany, through 

 which is inserted a brass cylinder at right angles to 

 the glass plates ; in this cylinder (which forms the 

 "well " of the Microtome) an accurately fitted brass 

 plug works, carrying on its top a flat-headed table- 

 like piece which entirely prevents the imbedding 

 agent from rising or turning round while the sections 

 are being cut. The plug is moved up and down by 

 a brass disc, which revolves between the block of 

 mahogany mentioned above, and a similar block 

 underneath. The brass disc is graduated on the edge 

 of its upper surface, each graduation representing a 

 movement of -0005 in. of the plug. The Microtome has 



a base-board which can be firmly clamped to a table, 

 and the whole is so conveniently arranged that every 

 operation or adjustment can be made at once, the 

 whole being in view on the table. The instrument 

 is beautifully finished, and fitted with a clamp into a 

 neat mahogany box. 



Carbolic Acid and Cement. — While working 

 in the Strassburg microscopical laboratories three years 

 ago, I mounted several fresh-water Algse in a weak 

 carbolic-acid solution, using asphaltum for the cement ; 

 their condition is still perfectly good. I would 

 suggest that after treating the insect in a strong 

 solution of carbolic acid, to produce the effects on the 

 chitine narrated by W. H., he should steep in a 2 per 

 cent, solution, then mount in the same solution and 

 cement with asphaltum ; the cell, if necessary, can also 

 be made of asphalt cement. — B. Sc., Plymouth. 



The Microscopical Society of Liverpool. — 

 At the last meeting of this society, a paper on the 

 " Larval Forms of the Echinodermata " was read by 

 Professor Herdman. The lecturer referred to the 

 somewhat isolated systematic position, and the wide 

 distribution in space and time of the Echinodermata, 

 and to the doubts which still exist as to their relation- 

 ship with other groups of the Invertebrata, He then, 

 after briefly describing some of the more important 

 anatomical peculiarities of the Echinoderm, proceeded 

 to discuss the embryology of certain members of the 

 five classes living in the seas of the present day. 

 Commencing with the Holothuroidea (or sea cucum- 

 bers), the development of Holothiiria tubidosa and 

 of Cuciimaria doliolum was traced, from the fertili- 

 sation of the ovum to the Auricularia stage, according 

 to the observations of Selenka. The characters of 

 the Auricularia were then discussed, and its metamor- 

 phosis through the pupa stage into the young 

 Holothurian described. The development of the 

 Asteroidea or star-fishes was exemplified by Prof. 

 Alexander Agassiz's investigation of various species 

 of Asteracanthion. The evolution of the Bipin- 

 naria and Brachiolaria stages was traced, and 

 their structure compared with that of the Auricu- 

 laria. Then the remarkable transformation of the 

 free swimming larva into the young star-fish was 

 briefly described, and the ultimate fate of the ciliated 

 processes discussed. The lecturer then passed on to 

 the Ophiuroidea (Brittle stars), and in Echinodea 

 (sea urchins), in which the larva has the form of a 

 Pluteus characterised by the possession of a large 

 post-anal lobe, and a provisional calcareous skeleton. 

 The recent investigations of Apostolides and others 

 were discussed, and the course of development of the 

 various larval organs was compared with that which 

 had been previously described in the Holothurids and 

 Asterids. In describing the metamorphosis of the 

 Pluteus into the adult Echinoderm, the importance of 

 Metschoukoff's recent discovery of the action of 

 Amoeboid mesoderm cells in absorbing temporary 



