OF THE PHYTOZOA. 117 



which it joins, by a septum representing the divisional membrane of each of 

 the contiguous cells. The state of things here is therefore quite different 

 from that in Volvox : for in the latter the cell-membrane is widely detached 

 from the protoplasmic nucleus, but the adjoining cells are adherent at all 

 points ; the intercurrent thi^eads are therefore v\dthin the cells, and uphold 

 an attachment between the nucleus and the cell- wall, — whilst in Gonium the 

 contrary obtains : the cells themselves are not in apposition, but held together 

 by a tubular extension from each angle ; and the nuclear protoplasm within 

 nearly fills the cell-cavdt}', and has no bands uniting it v\dth the waU — in 

 fine, the intercurrent processes of Gonium and of Volvox are not homologous. 



Besides the wall and processes just described, calculated to give strength 

 and resistance to the organisms, there are also the long cilia or filiform ap- 

 pendages known as filaments, flabella, or flageUa, seen at one extremity of 

 most Phytozoa, derived from the protoplasmic mass. To these are entirely 

 or chiefly due the locomotive powers of these beings ; they also act the part 

 of rudders in turning them on themselves, and in directing them hither and 

 thither. They do not belong to the class of vibratile cilia, but are larger, 

 filiform or whip-like, and have an undulating lashing movement. In some 

 cases they are many times longer than the organism to which they are attached 

 (XVIII. 15, 21, 22) ; and when two, as more frequently happens, are pre- 

 sent, they wiU often cross and intertwine. At times, in elongated forms, 

 they appear to be the mere terminations of the tapering-Hke extremity or 

 neck ; but the rule is, they do not proceed from the apex itself, but from one 

 side of it. Whei'e the species is encased in a fii^m integument, separated by 

 an interval from the central protoplasm, the filaments actually extend from 

 the latter and perforate the enclosed case ; in which, particularly when these 

 processes are fallen away, their points of issue are occasionally to be detected 

 b}^ depressions or by pores. Duiing frequent rapid movements these fila- 

 ments are not to be seen ; but when the motion is more gentle, or they are 

 at rest, or otherwise when colouiing matter is mixed mth the water, they 

 generally become visible. Even when their existence has not been noticed 

 duiing life, it may be sometimes demonstrated after the diying up of the 

 being, by the streak left upon the glass where it rested. Where more than 

 one or two filaments are present, their whirling, and the consequent agitation 

 of the fluid about them, makes their existence apparent. 



The number of filaments in Phytozoa varies. Two is the prevailing number, 

 which may or may not be of equal length ; but in not a few genera only one 

 is found, e. g. in Euglena, Monas, and Chilomonas, — whilst in others more than 

 two may be counted, situated together anteriorly, or some in front and others 

 behind. Where two are present anteriorly, it is not an uncommon arrange- 

 ment for one to extend in the direction of the long axis of the body, whilst 

 the other trails behind (XYIII. 12, 22, 23). 



MovEiiEXTs OF Phytozoa. — The motion of many Phytozoa is but slow, 

 and rarely intermitted ; in others it is more rapid and varied. It wiU be 

 modified by the figui-e of the organism and by the degree of firmness of its 

 waUs, with which it stands in inverse proportion. In Euglena the move- 

 ments are extremely varied and lively : the being is unrestricted in its 

 movements by an integument, and the contractile protoplasm has full scope ; 

 it is, in fact, in the condition of swarming gonidia, unenclosed by a wall of 

 cellulose. In many species of Monas and Bodo (Cercomonas), the motion is 

 irregular and peculiar ; it may be oscillating or rolling, at times leaping, at 

 others backward. Among the Vibrionia (XYIII. 57-69), an oscillating 

 spiral movement is a common characteristic, and either end may be advanced. 

 The revohing rolling motion of Volvocinece has for many years attracted 



