On the Conjugation of Amosba. 275 



had a lesson in mechanics. Every part of my machine (even to 

 the screws and smallest details) has been made by me without 

 assistance. I hope, therefore, some of your readers more favourably 

 circumstanced, may improve upon my first trials, and far excel me 

 in this beautiful and interesting art. 



My machine was originally planned for ruling micrometer 

 scales for use with microscopes and telescopes, .and its application 

 to ruling diffraction patterns (however beautiful) was quite a 

 secondary object with me, but Mr. Slack has, by his valuable 

 researches and papers, invested these ruled patterns with a practical 

 value and interest which I had not originally attached to them, 

 and as a microscopist I appreciate very highly the teachings 

 conveyed by his papers, showing the necessity of educating the eye 

 and judgment to enable the observer to interpret and correct the 

 illusory appearances so constantly met with in working under the 

 higher powers of the microscope. 



The Plate shows the machine with the self-acting machinery 

 added since Mr. Slack's paper. " This self-acting machinery consists 

 of a spring (from a musical box) driving a train of wheels and 

 pinions, ending in a fly, which regulates and controls the rotation 

 of the cam described by Mr. Slack, all the wheels and pinions being 

 (like the machine) made by my own hands, except one little steel 

 pinion which I purchased from a watchmaker." 



The machine is constructed for ruling lines from t-oVo^^ ^^ ^^® 

 TTTwo^li of an inch apart, and I have added to it the means of 

 further subdivision to the xWoo o^^ <^f ^°- i^^h ; but I have not yet 

 been able to procure any diamond fine enough for ruhng distinctly 

 more than about 5000 lines per inch. 



V. — On the Conjugation of Amoeha. By J. Gr. Tatem, Esq. 



I WISH to recall to the recollection of the members a paper brought 

 before them in a previous year,* " On Free-swimming Amoebje," of 

 which two species were described, but to which, under the impres- 

 sion that they presented phases only of Amoeba life no specific 

 names were assigned. I then stated " that we had no further 

 knowledge of Amoeba propagation and reproduction than that by 

 fission. An over-extended pseudopodum, perhaps larger than 

 common, remains attached to the spot to which it has been pro- 

 jected, separates from the parent mass and creeps off as an inde- 

 pendent living creature," and that this summary and somewhat 

 rude process, actively as it might be carried on, could only account 

 for the presence of a vast number of individuals within a limited 



* Vide ' M. M. J.,' June, 1869. 

 VOL. VI. X 



