24 THE VOYAGE OF H.M.S. CHALLENGER. 



An older larva abounded amidst the tentacles of the Australian form, and its 

 resemblance to the free-swimming Actinotrocha was at once apparent. 



In his description of the larva of the British form, Dyster appears to refer to the 

 prseoral lobe by his term abdominal division ; for he states that the " cephalic " segment 

 divides into three lobes, of which the lateral are longest. This probably refers to the 

 early condition of the ciliated arms of Actinotrocha. He has the merit of being one of 

 the few to see the early larval stages of this peculiar form. 



Very soon after the stage mentioned in the preceding paragraphs the larval 

 Phoronis swims freely in the water, and presents a large prseoral lobe or hood — the 

 mouth lying in the fold between it and the body, a stomach, and an anus. The 

 rudimentary arms soon appear ; indeed, in many, as above mentioned, they have the 

 form of blunt papillte arranged in a somewhat linear manner on the aboral face, before 

 the larval animal leaves the tentacles of its parent. The body and arms elongate, a 

 peculiar sac or pouch is formed in the ventral wall of the body just behind the arms, 

 and this rapidly enlarges so as nearly to fill the perivisceral cavity, and its inner wall 

 is rugose. The larval Phoronis now becomes quiescent, and suddenly the long pouch 

 is thrust outward through its opening in the body-wall, like the finger of a glove or 

 the proboscis of a Nemertean. Moreover, the loop of the alimentary canal slips into 

 the extruded pouch ; the larval body contracts so as to approximate mouth and anus. 

 The prseoral lobe slips into the oesophagus, leaving only a process — the " epistome." 

 The arms of the Actinotrocha-stage atrophy, and from a basal remnant the tentacles 

 of the adult spring. 



Homologies. 



Some of the earlier authors linked Phoronis with the Polyzoa, chiefly on account of 

 its lophophore ; though Professor Allman at once pointed out that, notwithstanding 

 the singular resemblance in certain parts of its structure between it and the hippo- 

 crepian Polyzoa, it had no real afiinity, " and must be viewed as a remarkable example 

 of representative form — of honiomorphism as distinguished both from homology and 

 analogy." He thought, indeed, its relationships lay rather with the Annelids, a conclusion 

 which Krohn and Schneider had arrived at with regard to the " Gephyrean worm," 

 resulting from the metamorphosis of Actinotrocha. Kowalewsky considered it neither 

 a Gephyrean nor a Polyzoon, but an enigmatical form approaching the worms, and 

 diverging from the MoUusks. Claparede,^ again, considered that the position of 

 Phoronis was between the Gephyrea and Bryozoa. The juxtaposition of mouth and 

 anus is a condition, he says, foreign to the Annelids, and much can be said in favour of 

 this view. 



External Form. — In external form Phoroms has little or no connection with any 



1 Annt'l. Chetop. Naples, p. 409, note. 



