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2. On the Anatomy of the Ampliioxus lanceolatus of YarrelL 

 By John Goodsir, Esq. Communicated by Professor Syme. 



After a short statement of the labours of Yarrell, Couch, Ret- 

 zius, and Miiller, the author gave a detailed description of the 

 structure of Ampliioxus, as observed in the dissection of one of two 

 specimens taken by Mr Forbes in the Irish Sea. The abdominal 

 folds, and the anterior and posterior anal fins, were described, and 

 the existence of a fin in front of the anus illustrated by an obser- 

 vation made by Professor Agassiz, of the temporary existence of 

 a similar fin in the embryos of certain fresh-water fishes. 



The osseous system presented two divisions, — the true or 

 neuro-skeleton, and the intestinal or splanchno-skeleton. The 

 true skeleton consisted of a chorda dorsalis, equally pointed at 

 both extremities, without the slightest trace of a cranium, and 

 destitute of any of the peripheral vertebral elements, with the ex- 

 ception of a rowof cells — germs of interspinous bones and fin-rays 

 — along the base of the dorsal and anal fins. The tissue of this 

 neuro-skeleton was not even cartilaginous, consisting merely of 

 membrane and globular nuclei, derived from the original elemen- 

 tary cells. The splanchno-skeleton consisted of a hyoid apparatus, 

 and of 70 to 80 pairs of elastic filamentous ribs. The hyoid ap- 

 paratus — in two divisions, with 17 pieces in each — exhibited 34 

 rays, pointing inwards, and each springingfrom one of the 34 basal 

 elements of the hyoid bone. These rays the author looked upon 

 as developments of the tubercles and teeth of the central 

 aspect of the branchial apparatus of the higher fishes, and not as 

 branchiostegal rays. The ribs were enveloped in the mucous 

 membrane of the intestine, and each alternate pair bifurcated 

 below, to enclose the abdominal longitudinal vessel or heart. 

 From these circumstances, and from other considerations, the 

 author looked upon the ribs oi Amphioxus not as true ribs, but as 

 splanchno-ribs — repetitions of the hyoid bone — analogues of the 

 tracheal and bronchial cartilages of the higher Vertel rata. The 

 tissue of the splanchno-skeleton is more advanced than that of 

 the neuro-skeleton ; the ribs are cartilaginous ; the hyoid bones 

 hollow cartilages, with isolated cells or nuclei in their interior. 



The nervous system presents nothing more than a spinal cord, 

 without a trace of cerebral development, and from CO to 70 pairs 

 of spinal nerves. The spinal cord was in the form of a ribbon, 

 pointed at both ends, with a dorsal median groove, and a line of 

 black or grey matter; was composed of nucleated cells, without 



