OF THE PHYTOZOA. 133 



germs which, whilst still wdthin the i3arent-cell, exhibit an oscillating move- 

 ment. He would even extend the phenomenon to all Monads ; yet we regard 

 it as no other than that of gonidial develojDment. Another circumstance 

 this same writer points out is, that in Monas Lens and allied forms, the 

 anterior individual produced by transverse self- division is 3 to 4 times 

 smaller than the posterior, and that in Tetramitus rostratus, where longi- 

 tudinal fission prevails, the right segment is much less than the left. It is 

 this unequal segmentation of Monads which induced Dujardin to represent 

 their multiplication to occui* by the detachment of a lobe or of an expansion, 

 and not by actual self- division : but in our opinion such a distinction is too 

 refined ; for the term self- division has a meaning wide enough to embrace the 

 phenomenon of fission whether by equal or unequal segments ; indeed the 

 latter variety is sufficiently common where no difficulty is felt in reckoning 

 it a mode of self-fission. 



In further elucidation of this act of segmentation in Monadina, we may add 

 the following remarks from Schneider {A. N. H. 1854, xiv. p. 327-328). 

 Speaking of Chilomonas Paramecium, this author writes — ''Whatever number 

 of these animals may be observed, no trace of division will ever be remarked 

 in them. Veiy rarely we may see two individuals adhering by their middle, 

 evidently produced by a longitudinal division. We shall endeavour to ex- 

 plain this. On close examination, one or two reddish lines may be seen 

 running backwards from the bottom of the indentation, which might readily 

 be taken for organs lying in the interior of the body. I have convinced 

 myself, however, especially by the comparison of the process of division in a 

 species of Bodo, that these lines indicate furrows, which gradually divide the 

 whole by cutting deeper and deeper on each side. As during this process 

 the animal undergoes no change of form, except in becoming a little broader, 

 and the division takes place along its whole length, the process must readily 

 escape obseiwation. The anterior end is always a little thicker ; the fuiTows 

 consequently are deeper and more distinctly recognizable in that part. With 

 a suitable arrangement of the microscope, it is evident that, the two furrows 

 being looked at simultaneously, two reddish lines are seen. It is only in 

 rare cases, when the division has taken place more slowly in some j^articular 

 spot, that the two specimens must endeavour to tear themselves free, and 

 thus, by twisting in contrary dii'ections, draw our attention to them. That the 

 process of division is effected in a similar manner in other Monadina, appears 

 from an observation of Ehrenberg's upon Cryptomonas cylindrica (p. 42) : — ' I 

 saw no instance of constriction or fissation ; but two individuals were swimming 

 whilst adhering together, which might lead one to suppose that a longitudinal 

 division from behind forwards had taken place.' And it is not improbable 

 that the specimen represented by him on tab. ii. fig. xix. 2, with two seminal 

 glands (nuclei?) and two longitudinal lines, was in the act of division." 



That Monads are only the first and simplest stage of existence of numerous 

 animal and vegetable organisms, is an undoubted fact ; but, if we may credit 

 some observers, their transformations are, in certain cases, very extraordi- 

 nary. Thus, Stein represents the nucleus of encysted VorticeUce to break 

 up into Monads (the Monas colpoda or M. scintillans), which by various in- 

 termediate stages become reconverted into VorticeUce. So, again, Hartig 

 {J. M. S. 1855, p. 52) and Carter (A. N. H. 1856, xviii. p. 122) represent 

 the conversion of Monads into Amoebce, the former by a coalescence of a group, 

 the latter by the simple assumption by individual Monads, on losing their 

 cilia, of polymorphism. Lastly, the resemblance of the zoospores of Achlya 

 to Bodo saltans has already been mentioned to be complete in ever}' respect, 

 save in the non-imbibition of colouring particles. 



