166 



Group Tubifera. 



Undt'i- the nbove name we may unite the three lollowing families, in wiiieli 

 tlie deseendiiig ciyptocyst forms or lalves part in forming a shorter or longer, 

 more or less complete, more or less insymmetrical tube, llie pnli/pidc lube, 

 the frontal wall of which from a deeper level ascends towards the aperture. 

 In all the members of this group a part of the cryptocyst descends more 

 or less deeply into the zoceciiint, generally in such a way as lo join the basal 

 wall with a shorter or longer basal edge on each side, i)ui in a few cases these 

 oulgrowtlis from the cryptocyst only reach the basal wall {SIctjdnojKirclUi lladiloni, 

 SI. liiislci) or the outgrowth on tlie one side only reaches the lateral wall (some 

 Thalainoporella-species). While tiie frontal wall and the lateral walls of the 

 polypide tube are always formed by the cryptocyst, the liasal wall is in most 

 cases formed by the basal wall of the zoo'cium, and in such cases the outgrowths 

 join this wall with a curved or angular edge on each side, the distally ascending 

 parts of which indicate the form and direction of the tube (PI. V, fig. 5 b, PI. YI, 

 fig. 5 d, PI. Via, figs, lb, 3e, 4 b etc.). More rarely the polypide tube has a 

 basal wall of its own, the two outgrowths from the cryptocyst bending round 

 and uniting within the basal wall of the zoa'cium, such forming a basal wall 

 for the polypide tube. In that case tlie two outgrowths join the basal wall of the 

 zoaxium in a continuous, curved or angular line and distally to this is seen the 

 tube shining through the wall (PI. VI, figs. 3d, 7 i, PI. Vic, fig. If). 



While in the Thalamoporellidae and in a few Steganoporella-specles (PI. V, 

 fig. 3 a) the frontal wall of the polypide tube is distally on each side in con- 

 nection with the lateral parts of the cryptocyst, this is not the case in the other 

 members of the group, in which this frontal wall (the »median process^ Harmer 

 in the Slcganoporellidae) is quite free. Thence follow^s, that in the TIkiIiuiio- 

 j)orellidae the >opesiul3e« are completely separated from the aperture while in 

 the other Tubifera they are fused together with it, bul this fusion can take place 

 in difTercnt degrees, and while in most species of the genus Sle<i(moporclla and in 

 the genus Aspidostoma the two opesialse are seen as two rounded sinuations from 

 the aperture, they are completely melted together with it in .S7. bilcr<dis and in 

 the genera Siphonoporelln, Labiopora and Cratcropom. 



In all such forms, in which the basal wall of the polypide tube is formed by 

 the basal wall of the zooecium, the opesiulse or the corresponding parts of the 

 aperture leads into two cavities (the » lateral recesses* Harmer), more or le.ss 

 completely sej)arated from the iioly])ide tube and from the remaining zocecial 



