REPORT ON PHORONIS BUSK II. 23 



Rudolph Wagener ; ' the general features of the body, the alimentary canal with what 

 he calls a hepatic dilatation anteriorly, and other doubtful organs being mentioned. He 

 noticed the rudiments of the permanent tentacles at the base of the larval tentacles ; 

 but he thought them mere appendages. C. Gegenbaur ^ next found some examples of 

 Miiller's Actinotrocha hranchiata towards the end of December at Messina, about 0'35 

 in. long, with fourteen tentacles ; while others appeared in February, 0"5 in. in length, 

 with twenty-four tentacles. He mentions most of the anatomical features formerh' 

 indicated, but added nothing to its relationships, for he was inclined to consider it the 

 larva of an Echinoderm. It was not until Krohn and Schneider found this larval form 

 undergo metamorphosis > into a Sipunculoid worm — which Kowalewsky somewhat later 

 showed was Phoronis — that, as mentioned in the introductory remarks, the true life- 

 history was ascertained. 



In the examples procured by the Challenger the free eggs in almost all cases seem 

 to have advanced beyond the earlier stages, and indeed to show various phases of 

 embryonic existence. The rounded forms had a diameter which ranged on each side 

 of l-240th of an inch, and thus the eggs of this large form are even less than those 

 of the smaller British species described by Dyster, who gave the diameter at l-200th 

 of an inch. An egg-capsule is sometimes difficult of detection in the preparations of 

 the extruded ova ; and all that can be said is that the exterior of the early forms 

 presents a definite pale margin, best seen in those, for instance, divided into a few 

 spheres, and with a central cavity in section, though in others a capsule is present. 

 The former condition was also noticeable in those at the gastrula-stage. Their develop- 

 ment would seem to be rapid ; indeed, Dyster states that in a few hours the surface 

 of the newly extruded products becomes ciliated all over, and the embryos are capable 

 of quitting the parent entirely at the end of the second day. The body-cavity of the 

 prseoral lobe is very early formed, the two cavities, archenteron and body-cavity of the 

 hood, apparently being seen in the section shown in PI. III. fig. 6. In outline many 

 of the embryos show at first an hour-glass constriction, and then a comma-shape, 

 apparently from the development of the prseoral lobe. In the stage shown in PI. III. 

 fig. 5, the prseoral lobe is on the right, and its body-cavity clearly outlined. The lobe 

 bends downwards over the mouth {m). The archenteron is indicated in the body on 

 the left, and also indications of the posterior body-cavity close to the upper hypo- 

 dermic border in the figure. Moreover, some show two or three papillte projecting 

 from the body of the larva, these representing rudiments of the tentacles, and they 

 appear to be proportionally large. 



In the embryos the hypoderm is very early difll'erentiated, and a thin pale line 

 beneath probably indicates the formation of the basement-tissue. The central cavity is, 

 moreover, lined with a distinct epithelium. 



1 Op. cit. 1847, pp. 202-206, Taf. is. « Zdtsrhr. /. viss. Zanl., BJ. v. p. 847, 1854. 



