PLATE IV. 



Fig. 1. Tentacular plume of Cephalodiscus, seen as a semitranslucent object. The line 

 ill tlie middle of the filaments indicates the axis or skeleton ; x 90. 



Fig. 2. Portions of the pinnse or filaments acted on by dilute potash so as to exhiliit the 

 central axis or skeleton, which at a has been exposed. The cellulo- granular 

 coating of the organs is hypodermic ; x 350. 



Fig. 3. Slightly oblique section of the bullions tip of one of the plumes, showing the 

 large globules and gland-cells. The hypoderm has intruded on the left, 

 showing that the slice has been made close to the base of the process ; x 470. 



Fig. 4. Transverse section of the tip of a plume just behind the foregoing, and while the 

 central lumen remains very distinct. The hypoderm shows somewhat regular 

 wedge-shaped divisions, as if composed of a single layer of large cells. The 

 wall of the central cavity presents numerous fibres projecting all round, as if 

 the reticulations were already commencing ; x 470. 



Fig. 5. Transverse section of the pedicle, showing the remarkable form usually assumed 

 by the elastic basement-tissue (bt) in contraction. The hypoderm (hp) occurs 

 externally ; and within the basement-tissue the large muscular fibres and 

 somewhat gelatinous connective-tissue fill up the central region. The small 

 dorsal and the large ventral incurvations are readily recognised, as well as the 

 two lateral ventral projections of the basement-tissue. The hypoderm on the 

 ventral surface has been somewhat stretched ; x 350. 



