86 



niake out the two generative pores (^. />.). Posteriorly to the inner edge of the left testis is seen 

 the vestigial rectum (r.), and between this and the central nerveus system is a conspicuous 

 blood-space (d.v.). The strand connecting this blood-space with the rectum may be a contracted 

 part of the vessel. 



Fig. 79 is a more or less sagittal section of an old male, in which however the proximal 

 end of the body was bent round in such a way as to be cut transversely, thus exposing both 

 the testes. Akhough the state of preservation is not all that could be desired, there can be 

 no doubt of the existence of the three body-cavities characteristic of Ceplialodiscits^ of a central 

 nervous system, and of a collar canal. 



Figs. 80 — 89 are sections nearly transverse to the long axis of the old male shewn in 

 fig. 75. Fig. 80, through the proboscis and the two arms, indicates that each of the latter 

 has a distinct central cavity. This cavity, which is continuous with that of the collar, is limited 

 by a definite basement-membrane, which in some of the imperfectly preserved male individuals 

 is exposed by the loss, by maceration, of the vesicle-containing epidermis. The membrane 

 probably has a supporting function, as in the arms of a normal zooid. The epidermic vesicles, 

 in this specimen, have a degenerated. appearance, and are not well stained. The cavity of the 

 left arm (Z. rt:.) shews distinct evidence of lodgitudinal muscles at the distal end, where it is 

 cut tangentially, and of fibres passing transversely across the cavity in the rest of its extent. 



Fig. 81, through the anterior part of the central nervous system {cji.s.), shews the cavity 

 of the left arm opening into the dorsal horn of the collar-cavity, here lined by a very definite 

 epithelium; a similar space occurring on the right side of the section. The space between the 

 two dorsal horns, and underlying the central nervous system, is the pericardium ; it contains a 

 considerable number of nuclei, the exact arrangement of which is uncertain. The next (more 

 dorsal) section shews some indication of the external part of the left proboscis-pore, though not 

 with sufficiënt clearness to justify me in asserting that proboscis-pores exist in the male. 



In the next section more ventrally (fig. 82) the pericardium no longer appears, and the two 

 collar-cavities are separated by a dorsal mesentery, at the ventral end of which an excessively 

 minute notochord is indicated. 



In fig. 83 the notochord is still visible, the right arm opens into the collar-cavity, and 

 the pigment-band of the proboscis has come into view. The proboscis is extremely muscular, 

 the muscles on the left side of its cavitj' being cut transversely. 



Fig. 84 cuts the mouth (/;/.) and the left collar-canal {c. c), behind which are the lateral 

 nerve and the left testis (A). 



Fig. 85 shews the right collar-canal, with the corresponding lateral nerve, and the pharynx 

 (///.) supported by a dorsal mesentery which carries a minute blood-space. This mesentery gives 

 off a branch to the left testis, while on the right side is seen the corresponding generative 

 pore {o-.p.), 



Three sections further (fig. 86) the alimentary canal has become very small. Both testes 

 are now seen, with the conspicuous dorsal vessel {d. v.), containing a coagulum and giving oft" 

 vessels to the testes. These travel along paths which may be regarded as lateral mesenteries, 

 similar to the lateral or ovarian mesenteries found in the female Ccphalodiscus. 



