92 E. PERCIVAL 



longitudinal muscles begin to atrophy and are seen in longitu- 

 dinal sections as mesogloeal bands striated with degenerate 

 muscle-fibres (PL 6, fig. 11, R.L.M.). The bands stain more 

 deeply than the rest of the mesogloea when treated with 

 Delafield's haematoxylin, 



Gastral Filaments. — About the time when the manu- 

 brium of the ephyra has become curled outwards the gastral 

 filaments first appear. They occur in pairs, one pair per inter- 

 radius (PL 6, figs. 1 and 5, G.F.). On each side of the columella, 

 and close to the exumbral endoderm, there grows laterally and 

 towards the central stomach an endodermal process (PL 6, 

 fig. 1, G.F.). Very soon the tip turns towards the oral opening 

 and remains pointing in that direction until the ephyra becomes 

 free (PL 6, fig. 5). Occasionally one or both filaments may be 

 suppressed. Thus, contrary to what has been maintained by 

 all writers hitherto, the longitudinal muscle takes no part in 

 the formation of the filaments which may be seen in a strobila 

 in various stages of development. 



Separation of an Ephyra from the Strobila . — 

 In passing upwards towards the oldest ephyra the connecting 

 strands are seen to become slightly stretched and the covering 

 epithelium does not stain so deeply as that lower down. They 

 converge to the apex of the exumbrella when the apical opening 

 has become obliterated. The closure of this opening takes 

 place comparatively early in the history of the attached 

 ephyra (Text -fig. 2), and a free disc having such an opening 

 may be considered to have been prematurely detached. Such 

 may happen in the laboratory when a strobila is roughly 

 handled. 



Shortly before an ephyra becomes separated it is seen that the 

 peristomial pits are very deep (PL 6, fig. 10, P.P.), and the depth 

 from the subumbrella to the exumbrella is much greater than 

 that in a younger disc. Also the columella is stretched so that 

 the gastral filaments are brought some distance away from the 

 exumbrella (PL G, fig. 5). The covering of this stretched portion 

 resembles in staining properties and cell-form that of the 

 connecting strand in the same condition. The longitudinal 



