ACROPTERIS. 



ACTINIAD^E. 



Fio. 1. 



ACRO'PTERIS (from Sxpos, a point, and ir-r4pis, a fern), a genus of 

 Ferns allied to Asplenium. 



ACROSALE'NIA, a genus of Fossil Echinodermata. (Agassiz.) It 

 occurs in the Isle of Sheppy. 



ACROSTICHON (from axpos, a point, and irrtxos, a row), a genus 

 of Ferns, most of which require stove heat in cultivation. The whole 

 of the species now referred to this genus are extra-European, being 

 inhabitants of the West and East Indies, and Australia. 



ACROTE'MNUS, a genus of Fossil Ganoid Fishes. A. Faba is found 

 in the chalk of Sussex. (Agassiz.) 



ACT'^EA. Under the name of SKTT), the Greeks described a medi- 

 cinal plant, which the moderns have ascertained to be what is now 

 called Samltui-n.1 Eljuiin. [SAMBUCUS.] Linnaeus applied the name to 

 a genus of perennial herbaceous plants found in various parts of 

 Europe, and the north of Asia, and America, belonging to the natural 

 order Banunculaeete, and only in a slight degree resembling the 

 species intended by classical authors. The genus thus understood is 

 known from all others of the Ranunculus tribe by its anthers being 

 turned inwards, so that when they burst the pollen may immediately 

 fall upon the stigma, while its flowers have only four sepals and 

 four petals. The properties of all the species are nauseous and 

 deleterious, as might be expected from their affinity to the poisonous 

 Aconite. 



One species, Act (fa picata, a common European plant, is found 

 occasionally in the north of Yorkshire among bushes ; it is popularly 

 called Black Baneberries and also Herb Christopher. It has purplish- 

 black juicy fruits, which would be dangerous from their tempting 

 appearance, if the fetid odour of the leaves did not prevent their 

 being touched. 



Another species, the A, cimicifuga, a North American plant, derives 

 its name from the belief that its fetid leaves have the power of driving 

 away bugs. 



ACTINIA. [AomriAD.*.] 



ACTINI'AD J3, a family of Helianthoid Polypes, having for its type 

 the old genus Actinia, the Sea Anemonie. It has the following 

 characters. Animal single, fleshy, elongate or conical, capable of 

 extending or contracting itself, fixed by its base, but with the power 

 of locomotion ; mouth in the middle of the upper disk, very dilatable, 

 surrounded by one or more 

 rows of tentacula ; oviparous 

 and viviparous ; marine. 



The internal structure of 

 the Actinia has been care- 

 fully investigated by Spix, 

 Teale, and others. They pos- 

 sess an alimentary cavity, 

 with a single aperture, 

 very large at the lower end, 

 and so elastic and contractile 

 that it can easily be turned 

 inside out. The cavity is 

 surrounded with flat muscles, 

 running lengthwise and 

 parallel. 



The egg organ (OMTMMB), 

 according to Teale's obser- 

 vations in Actinia coriacea, 

 forms elongated masses 

 attached along the inner 

 border of a series of organs 

 called leaflets, fig. 2, h. h. 

 *' Each ovary is composed of 

 several folds or plaits, which, 

 when unfolded, show this 

 structure to be about three 

 times the length it assumes 

 when attached to the leaflet, 

 By carefully spreading out 

 these folds, the ovary, with 

 the assistance of a lens, ig 

 seen to consist of two very 

 delicate layers of membrane, 

 enveloping a closely com- 

 pacted layer of ova After 

 enveloping the ova, the mem- 

 branous layers are placed in 

 appomtinn, and form a kind 

 of mesentery, by which the 

 ovary is attached to the in- 

 ternal border of the leaflet." 

 The Ar/iuiada; propagate all 

 thi: year round, although 

 perhaps in some species the 



Small Leathery Animal-Flower 

 (Actinia coriacea}. 



Fio. 2. 



Vertical ection of the above, to show its 



interior structure. 

 a a a. The skin. 



b. The base, by which the animal is fixed 



to the rock*. 



c. The three rows of feelers (tentacula). 



d. The mouth. 



f. The ptomach. 



/. I.'>nu r iturlin:il muscles, 



g. Point in which they unite. 



A A. The ovaries, which open by their ovi- 

 ducts into the stomach. 



'!< j"ited most abundantly in autumn. The ova are roundish, 

 and like those of polypes in general, are moved by means of vibratile 

 cilia, which cover their surface. After being discharged from their 

 move about actively for several days, during which they 

 -'o some change in form. They then relax their activity, the cilia 



HAT. HIST. DIV. VOL. I. 



Fio. 3. 



are absorbed, they attach themselves to a spot, aud pass through a 

 series of forms, before arriving at maturity. 



Although Spix has described in Actinia coriacea a nervous system, 

 this has not been confirmed by more recent observers. 



The habits of the Actinice have been studied by the Abbe" Dicquemare 

 and others. The forms of Actiniae vary according to their contraction 

 or expansion, presenting in- 

 numerable varieties. Their 

 expansion is said to be a more 

 certain indicator of fine 

 weather than the rise of the 

 barometer ; but this cannot 

 be practically taken advan- 

 tage of except during summer, 

 as the cold of winter drives 

 the Actinia from the shore to 

 the deeper waters, where the 

 temperature is more equable 

 and mild. On changing their 

 place of abode, some abandon 

 themselves to the mercy of ; 

 the waves, others creep along 

 the bottom, turning them- 

 selves inside out, and making " The ovaries greatly magnified. 



6. The oviduct. 



c. Egj-s. 



d. Ditto, with the first appearance of the 



embryo. 



e. Ditto, farther advanced. 

 /. Ditto, ditto. 



Fio. 4. 



Distribution of the nerves at the base of 



the Actinitc, according to Spix. 

 ft. The nervous ganglions. 

 6. Nerves. 



c. Nerves of communication between the 



ganglions. 



d. The longitudinal muscles. 



Fio. 5. 



use of their tentacula as 

 feet. When they find a 

 suitable place, they fix them- 

 selves, often so firmly, that 

 they cannot be detached 

 without tearing their bodies. 



Our distinguished English 

 naturalist, Ellis, has given a 

 very minute and, so far as it 

 goes, an accurate account of 

 these animals in the ' Philo- 

 sophical Transactions,' vol. 

 Ivii., part of which it may be 

 interesting to quote : 



" The lower part," he says, 

 " of these bodies have a com- 

 munication with a firm, 

 fleshy, wrinkled tube, which 

 sticks fast to the rocks, and 

 sends forth other fleshy tubes, 

 which creep along them in 

 various directions. These are 

 full of different sizes of these 

 remarkable animals, which rise 

 up irregularly in groups near 

 to one another. 



" This adhering tube, that 

 secures them fast to the 

 rock or shelly bottom, is 

 worthy of our notice. The 

 knobs that we observe are 

 formed in several parts of it 

 by its insinuating itself into 

 the inequalities of the coral 

 rock, or by grasping pieces of 

 shells, part of which still 

 remain in it, with the fleshy 

 substance grown over them. 

 This shows us the instinct of 

 nature, that directs these 

 animals to preserve them- 

 selves from the violence of 

 the waves, not unlike the 

 anchoring of mussels, by their 

 fine silken filaments that end 

 in suckers ; or rather, like 

 the shelly basis of the Serpvla, 

 or worm-shell, the tree-oyster, 

 and the slipper-barnacle, &c,, 

 whose bases conform to the' shape of whatever substance they fix 

 themselves to, grasping it fast with their testaceous claws, to with- 

 stand the fury of a storm. 



" When we view the inside of this animal dissected lengthwise, we 

 find a little tube leading from the mouth to the stomach, from whence 

 there rise eight wrinkled small guts, in a circular order, with a yellowish 

 soft substance in them ; these bend over, in the form of arches, towards 

 the lower parts of the bulb, from whence they may bo traced down- 

 wards to the narrow part of the upright tube, till they come to the 

 fleshy adhering tube, where some of them may be perceived entering 

 into a papilla, or the beginning of an animal of the like kind, most 

 probably to convey nourishment till it is provided with claws : the 

 remaining part of these slender guts are continued on their fleshy tube, 

 without doubt, for the same purpose of producing and supporting 

 more young ones from the same common parent. 



Longitudinal Muscles, with the feelers 

 (magnified). 



