6 BULLETIN OF THE 



formed (Fig. 10). Finally, in the adult, the nucleus of the cell, which 

 has been pushed centripetad by the multiphcation of fibrillse, comes to 

 lie opposite several pairs of radial rows or sheets of fibrillae. These 

 sheets always occur in pairs, the components of the pairs being separated 

 by a narrow clear space, and the pairs by broader spaces. 



As I have said, this musculature occurs throughout the entire stalk up 

 to the base of the calyx (Plate III. Fig. 19, mu.). I do not understand 

 on what ground Ehlers states ('90, p. 146) that in Urnatella "der 

 Muskelmantel in den gleichmassig dicken Stengelgliedern nicht deren 

 ganze Lange erfiillt." 



There is a considerable difference between my description of the struc- 

 tures of the muscle fibres and that of Ehlers ('90, pp. 25-28) for Asco- 

 podaria. In the latter case, the muscle cells are placed three to five 

 deep, instead of in one peripheral series, as in Urnatella. Moreover, in 

 Ascopodaria the fibrillae lie in two thick peripheral bands on the sides 

 of each muscle cell ; whereas in Urnatella several muscle bands (each 

 consisting of a single row of fibrillse) belong to each cell. 



The differences between the two genera are easily explained by assum- 

 ing an increase in the number of muscle cells in Ascopodaria, so that 

 they can no longer lie in a single peripheral series, and that the fibrillae 

 bands have become greatly crowded together, so that one band is not 

 equivalent to a single band of Urnatella, but to all of the bands of Urna- 

 tella which have arisen on one side of the cell. The stalk musculature 

 of Ascopodaria is thus more highly developed than that of Urnatella. 



Ehlers mentions the resemblance between the muscle fibres of Ascopo- 

 daria and those of Nematodes, especially the Coelomyaria. 



I have referred above to vibratile movements in the living stalk. 

 Stained sections show, placed more or less abundantly throughout the 

 stalk, elongated spaces terminating blindly at one ^nd in structures 

 which must be regarded as flame cells (Plate II. Fig. 12, cl. Jim.). 

 Such a flame cell is spherical in form, stains slightly, possesses a large 

 nucleus, and gives off into the elongated space cl. tb. the well known 

 cirrus (Wimperfiamme). 



The form of the cirrus in all cases examined was conical, the axis 

 of the cone being usually thrown into a sigmoid curve. Where the 

 cirrus arises from the cell, it is slightly constricted, then enlarges sud- 

 denly, forming a thickened ring. Distal of this ring the cirrus tapers 

 gradually to a fine point. That the cirrus is composed of a number of 

 agglutinated cilia is indicated by the presence of longitudinal striae. I 

 believe that the flame cell closes the lumen of the tubule at this point. 



