THE 



MONTHLY MICROSCOPICAL JOURNAL. 



DECEMBEK 1, 1873. 



I. — Fuiiher Researches into the Life History of the Monarls. 



By \V. H. DALLDiGER, F.R.M.S., and J. Drtsdale, M.D. 



(Bead before the Eoyal Microscopical Society, Xov. 5, ISTo.) 



Plates XLI., XLII, and XLIII. 



In the farther pursuit of our inquiries we have succeeded in 

 working out the morphological history of three forms which we 

 believe have been hitherto undescribed. 



The striking similarity of form and structure in all the ex- 

 tremely minute monads makes distinction of form almost impos- 

 sible, whilst the tendency of individuals to vary from the type-form 

 makes it unsafe. But physiologically and morphologically the 

 recurrent cycle of sequence is unerring. 



The form to which the following description applies, is found in 

 vast numbers in the putrefying fluid resulting from the maceration 

 of any of the Gadida; ; but it rarely appears until the maceration 

 has proceeded for two or three months, and is always yielded most 

 freely by the decomposition of the head. 



Its average length is about the a^rroth of an inch. In form it 

 is a long oval, inchned to an egg-shape. Its general form is seen 

 in Fig. 6. PI. XLI., and Fig. 1, PL XLII. At one end, generally 

 the narrower, a sharp conical projection is found as in h, Fig. 6, 

 PI. XLI. ; in the majority of cases it is curved, and from it a fine 

 flagellum, from one and a half times to twice the length of the body, 

 proceeds. Lender this, and at a httle distance from it, e, Fig. 6, 

 another and longer flafjeUum arises, and with this the monad 

 anchors itself to the covering glass, and constantly springs back- 

 wards and forwards by its iift-urrent coil and uncoil, reminding 

 the observer of the vorticella, except that the uncoihng is as rapid 

 as the coiling. Fig. 1, PL XLII., shows the coiled condition at a, 

 the imcoiled state at c, while h is intermediate. It is possessed of 

 a nucleus-like body, always at the end of the body opposite the 

 proboscis, and a few vacuoles are scattered over the sarcode. 



The commonest phenomenon exhibited by this form is its 

 remarkable mode of fission. The first indication that it is about 

 to proceed is given by a slight constriction as at a. Fig. 6, PI. XLI., 



yoL. X. u 



