LECTURES ON EMBRYOLOGY. 



37 



XXXIV VEBETILLHM.J 



[PLATE XXXVI-RKTEPORE 



Vv e nave ucre Umgrauia (<me ot wuicia, Vtretil- 

 lum, is given in Plate XXXIV) of the principal 

 groups of this class; and indeed there is scarcely 

 one family of Polypes of which these diagrams do 

 not represent some species. The Corals are among 

 those which have from the beginning been consid= 

 ered as a type belonging to the class of Polypi. 

 And various species are represented here ; among 

 them are stems, branching and supporting soft lit- 

 tle animals, which come out like flowers. 



The variety of these beings is such that indeed 

 they rival, by their glorious colors and variety of 

 form, the most brilliant fiowers of the dry land. 

 Such as this Actinia are common on these shores, 

 and have also universally been considered as Poly- 

 pi ever since these beings have been combined 

 into one class, and have been separated from the 

 vegetable kingdom, 



Jt, would carry me too far if I were to give now 

 the full history of the knowledge successively ac 

 quired upon these animals, and to refer io those 

 views of these beings which were entertained by 

 naturalists at the time when some w^re supposed 

 lo be simple mineral concretions, and others were 

 considered as marine flowering plants ; the ani- 

 mals upon the stems being mistaken for flowers, 

 and the stems compared to the stems of plants. 



But after it was ascertained that there were con- 

 tractions taking place in the soft parts, that there 

 was an internal cavity into which food was intro- 

 duced and digested, no doubt could remain as to 

 the animal nature ef these beings; and all small 

 animals whose upper opening is surrounded by 

 tentacles, and which are grouped together upon 

 a common stem, were at once referred to that class. 

 And some simple animals, like the Actinia, were 

 also referred to the same class, being considered 

 as isolated forms of the same character. But we 

 gee upon the following Plate (Plate XXXVI) 

 one of these coral like stems, (Retepora) with mi- 

 nute openings, in which numerous animals are 

 contained, whose structure has been investigated 

 by MM. Audouin and Milne-Edwards, and has 

 been found to differ so materially from that of 

 Polypi, that this type, of which there are various 

 forms, is now generally considered as belonging 

 (G the great division of Mollusca, although they 



compound animal. All the investigations 

 which have followed since this suggestion was 

 first made, have only gone to confirm the view, 

 that these porous animals do not belong to the 

 class of Polypi, but to a higher type, and indeed 

 resemble in some respects even the oysters, the 

 clams, and still more the compound ascidiag, in 

 whose vicinity they will in all probability be placed 

 forever, showing that compound animals may be- 

 long to ali great groups of the animal kingdom, 

 and even occur as anomalies among mammalia, 

 in the shape of twins. 



[PLATE XXXI ALCYONIUM AND RKNILLA ] 



Oilier Uia.Mra.ms repreaeiu various oiuer types. 

 Here, (PI. 30) for instance, the beautiful Tubulariaa 

 are seen forming most beautiful flower-like animals 

 uniting in bouquets upon the old logs and swim- 

 ming lumber which are fastened in the water. 



Two species of this kind are very common 

 around the city of Boston. One (Plate XXX, fig. 

 G) with a larger crown, occurs in great abundance 

 upon the logs in Craigie's bathing house ; another 

 smaller species is found almost everywhere upon 

 old logs, The larger is about two or three inches 

 high, and the crown, when fully expanded, about 

 one inch in diameter. 



This diagram, (Plate XXXI, fig. A) represents 

 another still undescribed species, with compound 

 stems, from Boston harbor, belonging to the fam- 

 ily of Alcyonium, in which every one of the indi- 

 viduals terminates with a star of eight fringed ap- 

 pendages or tentacles (fig, B). The most curious, 

 however, is this one (fig. C), a Eenilla, which t 

 collected in Charleston, S. C. an animal with a 

 soft body of a hollow stem, sticking in the wet 

 sand, with a large disc, spreading above which* 

 seen from below, shows lateral dilations, front 

 which, upon ths upper surface, arise a great 



