PLATE VI. 



Fig. 1. Longitudinal section of the tip of the pedicle of an adult Cephalodiscus, 

 showing the attachment of a young bud just above the terminal surface 

 (which is somewhat sucker-like) ; Im, strands of longitudinal muscles ; hps, 

 modified hj^poderm forming the terminal surface of the j^edicle ; gm, section 

 of a young bud, showing the central chamber (ch) continuous with the axis of 

 the pedicle of the adult ; x 850. 



Fig. 2. Transverse section of an adult Cephalodiscris through the region of the mouth 

 (m) and ovaries, one pigment-mass (od), however, only having been cut. The 

 buccal shield (bs) on the right is seen folding over dorsally {hs}:)), so as to I'un 

 into the tissues at the bases of the plumes (hi-) ; g, grooves at the bases of 

 tlie lophophoral arms. The notochordal region lies between this letter and m, 

 though the notochord is not seen in this section. The mouth is observed at 

 (m) and the pharyngeal region with its numerous folds and a gill slit (gs), 

 while on the left is a section of the j)ost-oral lamella (j^l) with its central cavity 

 or chamber ; 7', greatly distended rectum ; od, pigment of oviduct ; oi\ large, 

 and ov', small ova, with nuclei and nucleoli ; x 90. 



Fig. 3. Transverse section of the shield and dorsal region in the long axis of the central 

 region of the nervous system (wc). The thick coating of hypoderm (hp) 

 bounds the latter externally, while internally it rests on the basement-tissue (ht.); 

 hp, sections apparently of the shield-pores in their progress inwards ; hsm, 

 radial muscles of the buccal disk or shield; hs, hypoderm of shield; od, position 

 of the pigment of the oviducts ; x 210. 



Fig. 4. Transverse section of the same bud as in PI. V. fig. 4, in the anterior region, so 

 as to strike the commencement of the nerve-centre («c), with the central 

 cavity (c). The young plumes are irregularly cut from their variable position, 

 and the sides of the disk fold over into the basal region of the plumes. The 

 large size of the terminal process of the plumes is well seen in the larger 

 organ ; x 210. 



Fig. 5. Section a little behind the foregoing, giving the nerve-centre {nc) in full develop- 

 ment, under the thick hypodermic coat Qip), while the tip of the anus [an) 

 has also been included ; cva, collar space going to plumes ; hsm, radial muscles 

 of buccal disk ; c, region of the notochordal. The plumes are more widely 

 separated in this region, and the young filaments have the form of hypodermic 

 papillse ; X 210. 



Fig. 6. A somewhat oblicpie section through the buccal shield {hs) and the post-oral 

 lamella {pT) with its central cavity, to which the dotted line goes. Beneath is 

 a collar pore (cp), which is, however, indifferently shown in this section. The 

 nerve-centre {nc) and a pore {hp>) leading into the cavity of the shield are also 

 cut, the two 1)ody-cavities of the region lying above the former {nc) in this 

 view, that is ventrally in nature. The other parts are an ovary {ov) and a 

 portion of the pigment-mass of an oviduct {od) ; x 90. 



