434 Unifcrnihj of California Publications in Zoology [VOL. 19 



Just as the anal cirri with their attached fibers frequently persist 

 intact after the remaining cytoplasm has dissolved, so also do the mem- 

 branelles with the membranelle fiber resist immediate disintegration. 

 Furthermore, in seven recorded instances I have observed the anal 

 cirri, their fibers, the motorium, the membranelle fiber, and the nn 111- 

 branelles, all remain united for several seconds to about three minutes 

 after the disruption of the body. In three of these cases, the anal cirri 

 and membranelles continued lashing, but feebly and for a few seconds 

 only. 



The motorium with its attached jiirmbnnielle and anal cirri fibers 

 has been distinctly identified after more or less complete disintegration 

 of the body. Much more frequently, however, only the fibers are 

 evident. It would appear, therefore, that the motorium readily 

 detaches itself from its connected fibers or otherwise vanishes, perhaps 

 by rapid dissolution. In its normal position the motorium may be 

 readily displaced with the needle-point. However, it resumes its usual 

 position upon the removal of the needle. But if it be pushed too far, 

 say ten microns, out of place it may become detached from its fibers, 

 or apparently injured to such an extent that it dissolves or otherwise 

 disappears. 



In unstained animals, as stated previously, the membranelle fiber 

 may be distinctly seen only a short way from its attachment to the 

 motorium. Thereafter it becomes concealed among the ectoplasmic 

 granules along the basal plates of the membranelles (fig. 17). It may 

 be observed only after these granules have dispersed with the dissolu- 

 tion of the ectoplasm. Its general physical properties are apparently 

 the same as those above stated for the anal cirri fibers. That descrip- 

 tion may suffice for this fiber also. 



However, associated with the membranelle fiber and membranelles, 

 certain plates have been found which I shall here call the "mem- 

 branelle fiber plates" (fig. 13). These were first clearly observed upon 

 partial disintegration of the series of membranelles which had been 

 dissected from an animal vitally stained for about eighteen hours in 

 a .0001 per cent aqueous solution of haemotoxylin. The membranelles 

 proper had been set free, thus exposing these plates, one for each 

 double row of membranelles. Figure 17 is a camera drawing of the 

 plates and the membranelle fiber. The spokelike formation shown in 

 the figure is usually assumed by the series of plates upon detachment 

 of the membranelles and disintegration of the ectoplasm. This 

 arrangement is clearly occasioned by their individual attachment at 



