2l6 



SCIENCE- GOSSIP. 



the creature has a span of 7 inches. The sexes are 

 separate, and the genital organs are situated not 

 in the body disc, but in the tiny pinnules of the 

 arms. The* fertilised ova are set free as barrel- 

 shaped embryos -which acquire four encircling 

 bands of cilia. Next appear a few minute cal- 

 careous plates within this embryo, forming, as it 

 were, a tiny cask set upon a tiny stalk. Free- 

 swimming life being now almost ended, a disc 

 containing a perforated plate appears on the lower 

 extremity of the stalk : and by this, attachment is 

 made to any object that happens to be in the way. 

 The soft, barrel-shaped mass of the swimming 

 larva has now shrunk and adapted itself to the 

 form of the enclosed calcareous skeleton, and the 

 creature is fairly launched upon the stalked and 

 anchored period of its life. In this stage the 

 skeleton is made up of a basal plate, rooting the 

 animal to its host, a considerable number of joints 

 set end to end forming a stalk upon which is 

 seated the cup-shaped framework of the body, con- 

 sisting of two circles of large perforated plates. 



rudirrjerjtar^ 



calcareous 



plate.5. 



Fig. 7. Stalked larva of Antedon. 



respectively the " basals " and the " orals." The 

 former form the base of the cup. and the latter the 

 upper ones. Growth after this is rapid; other 

 circles of plates appear, the ten arms proceed from 

 one of the circles, the top joint enlarges into a 

 plate-like structure and develops claw-like jointed 

 organs, the cirri. The body breaks off from its 

 stalk and becomes free to creep among the rocks 

 at will, or swim gracefully with rhythmic beats of 

 its long feather-like arms. Special interest attaches 

 to this beautiful creature from the great part 

 played by its relations, if not its ancestors, which 

 lived during former periods of the earth's history, 

 for the Encrinites, whose remains contributed so 

 greatly to build up the huge masses of our 

 mountain limestones, were but gigantic Penta- 

 crinoids of structure practically identical with 

 the stalked larva of Anted on (Homell). Dr. Car- 

 penter's " Microscope " has a good plate of the 

 rosv feather-star. Mv remarks have been largrelv 



taken from " Gosse " and from CasseLVs " Natural 

 History. " also from Hornell's "Journal of Marine 

 Zoology " ( 3 ). 



MICROSCOPY FOR BEGINNERS. 



By F. Shtllis-gtox Scales, F.R.M.S. 



[Continued from p. 186.) 



Objects to be mounted in glycerine jelly or any 

 similar medium can be transferred directly from 

 water, but those to be mounted in Canada balsam 

 must be first thoroughly dehydrated, and this is 

 done by transference to one or two baths of 

 methylated spirit, alcohol having a strong tend- 

 ency to absorb water. In some cases — as, for 

 instance, with insects that require arranging — 

 the object should be arranged between two slides, 

 tied together with two slips of visiting, or thicker, 

 cardboard between the ends, and the whole im- 

 mersed bodily for some hours in the methylated 

 spirit. The spirit has a tendency to harden the 

 structure, so it is necessary to do the arranging 

 in this way beforehand. The object may then be 

 •• cleared " of alcohol by transference to clove oil. 

 and thence to a final soaking in turpentine ; but 

 in most cases the clove oil may be omitted, and 

 the object simply transferred from the methylated 

 spirit to turpentine. From the turpentine the 

 mounting in Canada balsam may be proceeded 

 with, as already explained in detail. (See ScTENCE- 

 Gossip. vol. vii. pp. 122 and 151.) "We would 

 again lay stress upon the fact that whilst the 

 turpentine stage always immediately precedes 

 mounting in Canada balsam, and the object must 

 be freed from every trace of water, the reverse is 

 the case when mounting in glycerine jelly or 

 similar media, as the object must then receive its 

 final soak in water, and be free from every trace 

 of turpentine, etc. 



The great value of staining is not to make 

 •• pretty " objects for the microscopic cabinet — 

 beautiful as the effects often are — but to differen- 

 tiate the structure. This has now become a high 

 art. and new methods for special purposes are 

 being constantly introduced, especially in histology. 

 With these the beginner has nothing to do, though 

 the time may come, when he is no longer a 

 beginner, when he can refer to larger or special 

 works dealing with the subject, around which so 

 voluminous a literature has already grown. Of all 

 stains, haeniatoxylin (the active principle of log- 

 wood) is the most generally useful, especially for 

 vegetable sections. It is best purchased from the 

 optician's in an alcoholic solution, and improves 

 greatly with keeping. Before staining, many ob- 

 jects, such as vegetable sections, may require 

 bleaching. Steeping in alcohol will generally 

 have this effect ; but a solution of chlorinated 

 soda is an excellent bleaching agent, without being 

 too powerful. It is made as follows : One ounce 



( 3 1 Witb regard to tbe drawings with which we have endea- 

 voured to illustrate the foregoing notes, we may say that 

 figs. 1, 2. 4 and 5 are after figures in Mr. Hornell's most 

 interesting and well-illustrated "Journal oi Marine Zoology,"* 

 now unfortunately in abeyance : fig. 3 is after one in Nichol- 

 son's •' Manual of Zoology " ; fig. 8 is drawn from a slide in our 

 possession, anil fig. 7 is after a figure in Glaus and Sedgwick's 

 •• Text-book of Zoology." — Ei>. Microscopy. 



