68 



KNOWLEDGE, 



[Maech, 19C2. 



PRESERVING AND MOUNTING ROTIFERA. 



1?_V Chaules F. Koussklet, Cnnilor, B.M.S. 

 For Note referrimj to Material, see the MirroKCopy Culumn. 

 There be low observers of jtond lil'e wIki liavc not felt 

 i) keen desire to i)reserve aud keeji these small lii^'lily- 

 (>ri,Muised s|iarks of life instead of lettini^ them die and 

 disai)i)ear in a few days. For a close study of this s''oup, 

 well preseryed type specimens are of the j^reatest possible 

 assistance and inijiortanee. and if such had existed formerly 

 much confusion an<l inexactitude in their description and 

 classification would have been avoided, i)articularly in 

 the s'V'"" of three or four different names to the same 

 species, which causes so much trouble to the student. 



The total abseuce of type specimens of Rotifers to refer 

 to when required originally led me to attemjit to produce 

 them, and it is now over ten years since the first successful 

 exjieriments at preserving them in a fully extended aud 

 natural state were made. My method, although so simple 

 now, took fully three years to work out until the right 

 aud most suitalile narcotic, fixiug agent, and preserviug 

 fluid were found. By the use of suitable fixiug agents, 

 not only the external shape of Rotifers can be preserved, 

 but also all the internal structure to the minutest 

 anatomical details, such as the striated muscle fil)res, 

 nerve threads, vibratile tags or flame cells, sense hairs, 

 cilia, etc.,, and frequently important details can be more 

 readily ob.served than in the living animal. 



As is well known, no killing agent is sufficiently rapid 

 to prevent the complete retraction of Rotifers, and few 

 other animals can contract into such a shapeless mass 

 when we attempt to kill them by ordinary means, such as 

 poisons, alcohol, heat, etc. It is, therefore, necessary to 

 use first a suitable narcotic, which has been discovered in 

 hydrochlorate of cocaine. As a result of many trials, the 

 best solution for most Rotifers has been found to be the 

 following mixture : — 



2 % solution of liydrochlorate of cocaine, 3 parts ; 

 Alcohol (or methylated spirit), 1 part.; 

 Water, 6 parts. 



Another narcotic which is also very suitable for Rotifers 

 is a one per cent, w^atery solution of hydrochloride of 

 eucaine, recommended by Mr. G. T. Harris, for Infusoria 

 and other animals. These narcotics, even so dilute, are 

 not to be used {sure, as they would cause the Rotifers to 

 contract at once and not expand again. The principle to 

 be followed throughout is to use the narcotic so weak that 

 the animals will not mind it at first, but continue to 

 expand or swim about freely. After a short time its effect 

 will make itself felt on their nervous system, aud then 

 some more of the narcotic may be added, until complete 

 narcotisation is produced, or until the animals can be 

 killed without contracting. 



But before the operation of narcotising is begun, it is 

 very necessary to isolate the Rotifers in perfectly clean 

 water. The best way is to pick them up under a dis- 

 secting microscope by means of a very finely drawn-out 

 pipette, having a funnel-shaped enlargement at the other 

 end, which is covered with an elastic membrane. This 

 pipette forms a most delicate syphon, by means of which 

 any selected Rotifer can readily be taken up with the 

 least quantity of water, and transferred to another trough 

 or -watch-glass full of clean water. This preliminary 

 precaution is necessary, because particles of dirt in the 

 water readily attach themselves to the cilia of dead 

 Rotifers, rendering them unsightly under the microscope. 

 Another advisable precaution is to separate the different 

 species, because most sjiecies rcquii-e a slightly different 

 treatment, and because the small species too readily 

 adhere to the cilia of the large species. 



Having then isolated a number of frce-.siniinming 

 liotifers in a watch-glass half full of perfectly cli-an water, 

 one drop of one of the above narcotics is added and well 

 mixed. After five or ten minutes, if the animals continue 

 to swim about freely, iinother drop is added, and so on 

 until the effect of the narcotic becomes visible, and until 

 the motion of the cilia, or the movements of the animals 

 slacken or almost cease, when they are ready for killing. 

 The effect of the narcotic varies very much with different 

 species, some are most sensitive to it, whilst others can 

 stand a consideralile quantity for a long time. Some 

 ])ractice and patience are certainly required to find out 

 the right time to kill the diiferent species; no general 

 rule cau be given, as the time may vary from 1.5 minutes 

 to seviTal hours. It is very essential, however, that the 

 Rotifers be still living when the killing fluid is added to 

 prevent post-mortem changes in the tissues which begin at 

 once on the death of the animals. [To be continued.) 



Conducted by M. I.Cro§s 



PoMi-i.iFE Coli.kctint; in M.\Rru. — The same species as 

 those mentioned for February are still to be found and in greater 

 abundance. .Some new Icfusoria will hare made their appear- 

 ance, such as Stent'/r puli/morpliiis, which will be found 

 covering the rootlets of Duckweed and other submerged plants, 

 Peridiii'ntm lahvhiluin and the free-swimming colonies of Sijnura 

 ticel/a, etc. Then the very minute and beautiful colonies of 

 Collared Monads, Codosifja umheUata, and other species of this 

 group may be looked for, attached to the stems of Vorticella trees. 



All the Rotifera forming the winter fauna will become very 

 abundant in March, and as the food supply in minute Algae 

 and Infusoria increases, fresh species make their appearance 

 with every rise of temperature. The following additional 

 species may be looked for: Brachiomin diii/iilarix ; Xothnlra 

 acuiiih.uta, sp/Hifera, and Jnhis ; Eurlilania orophu : Diiiorharis 

 jmcillttm ; lJ!asc]ii:a lucinulata ; Proalex drripiens and prlro- 

 myzon ; Monoslijla corniila, Di(/!eiia f'orcijiala : liot/fer cidr/aris. 



Tetstiiif/ Objfctiri's. — To judge decidedly for oneself whether 

 an objective is a good, bad, or indifferent one is a matter that 

 calls for more than ordinary discrimination, and there are but 

 few workers whose judgment as to the merits of any particular 

 lens would be accepted without reservation. 



It may almost be said that the microscopist who is capable of 

 judging lenses is born and not made, for while some can almost 

 by intuition give an opinion which will ultimately prove correct 

 at almost the fu'st sight of a favourite object through the 

 objective, others who have had perhaps excellent opportunities 

 of acquiring skill are unable to arrive at a reliable decision. 

 Practice, on projier lines, will however greatly assist in 

 estimating the quality of lenses, and it will be well to enquire 

 what the elements of a good objective are and what tests can 

 be applied to determine without doubt whether or no it is 

 accurately constructed and of good ])erformancc. 



The qualities of an objective depend particul.arly on centreing, 

 corrections for chromatic and spherical aberration, aud accuracy 

 of manufacture. Beyond these, numerical aperture and initial 

 magnifying |)ower require consideration. 



"We will assume for our ]nir])0se that the objective is made 

 on a good formula and is constructed ou rational modern 

 principles such as are adopted by all up-to-date opticians, and 

 proceed to consider the tests that may be a]iplied. For the 

 majority of o]>tioal instruments, standards arc set, and if the 

 specimen under examination conforms to that standard or ia 

 equal to it, it is considered satisfactory, but the microscojje 



