337 



DICTYOGEN^E. 



DIGESTION. 



333 



areolate spinous shield, and differ so much from the other forms of 

 Diatomacece that many naturalists have doubted the propriety of 

 placing them there. The species are numerous, the larger number 

 being fossil and found with various forms of Diatomacece. 



DICTYOGENJE, a class of Plants, proposed by Liudley, and 

 adopted in his ' Vegetable Kingdom.' It embraces a number of orders 

 standing between the larger classes of Exogens and Endogens. They 

 have a monocotyledonous embryo, but they have also a broad net- 

 veined foliage, which usually disarticulates with the stem. The 

 following are the natural orders of Dictyogence : 



Triuridacew. 

 Dioscoreaccce. 



Smilaceai. 



Philcsiacece. 



Trilliacco!. 



Roxburghiacece. 



Flowers unisexual. Perianth free. Carpels 00 ; 

 one seeded 



Flowers unisexual. Perianth adherent. Carpels 

 consolidated ; several seeded .... 



Flowers bisexual. Carpels several, quite conso- 

 lidated. Placenta; axile. Flowers hexapeta- 

 loideous 



Flowers bisexual. Carpels several, quite conso- 

 lidated. Placentas parietal. Flowers 3-C- 

 petaloideous ....... 



Flowers bisexual. Carpels several, half consolidated. 

 Placentae axile. Flowers 3-petaloideous . . 



Flowers bisexual. Carpels solitary, simple, many- 

 seeded, with long-stalked anatropal seeds, and 

 a basal placenta 



DICTYOPHYLLIA. [MADREPHYLLKEA.] 



DICTYOPHY'LLUM, a genus of fossil Plants, proposed by Lindley 

 and Button ('Fossil Flora') to include a large specimen (D. crassi- 

 nemum) from the New Red-Sandstone of Liverpool, and a more 

 delicate species (D. rugosum) from the Oolitic shales of the Yorkshire 

 coast. The latter is regarded as a fern by later writers. Its nervures 

 are rudely reticulated. 



DICTYOTACE^E. [ALG*.] 



DICYPELLIUM, a genus of Plants belonging to the natural order 

 l.'tHcixxac. It has dioecious flowers, with a deeply 6-parted spread-out 

 calyx, with equal permanent segments. The staminiferous flowers 

 have 3 rows of sterile stamens ; the 3 outer being perfectly petaloid, 

 the 3 next petaloideo-unguiculate, indexed at the point, with 4 pits 

 below the point ; the 3 inner compressed, sessile, truncate, with 2 pits 

 on each side below the point, and 2 glandular protuberances at the 

 back. The fruit is dry, and seated in the enlarged, fleshy, shrivelled 

 calyx, and among the enlarged, hardened, sterile stamens. The 

 inflorescence consists of single few-flowered racemes. 



D. caryophyllatum, Bois de Rose, has alternate oblong leaves 

 tapering to a very fine point, which is nevertheless bluntish, acute 

 at the base, papery, and smooth-netted on the under side. It is a 

 tree, and a native of the woods of Brazil and Guyana. It is culled 

 Licari Kanali by the Caribs ; and is the Licaria Guianentit of Aublet. 

 The bark gives out a smell very like cloves, and has a hot, clove-like, 

 peppery taste. It is used as a medicine by the natives in the coun- 

 tries where it grows, and possesses powerful tonic properties. 

 (Lindley, Flora Medica.) 



DIDELPHINA, a sub-family of Mai-mpiaia. The whole of this 

 sub-family have the inner toe of the hind foot converted into a 

 thumb, destitute however of a claw, and this development is appa- 

 rent in nearly all the species which have a scaly prehensile tail. 

 Professor Owen remarks that in some of the smaller Opossums the 

 sub-abdominal tegumentary folds are rudimental, or merely serve 

 to conceal the nipples, and are not developed into a pouch ; and 

 in these the young adhere to the mother by entwining (heir little 

 prehensile tails around hers, and clinging to the fur of her back; 

 whence the specific name dortigera, applied to one of the species. 

 He further observes that few facts would be more interesting in 

 the history of the Marrupialia than the condition of the new-born 

 young, and their degree and mode of uterine development in these 

 Opossums. Since the Marsupial bones serve not, as is usually 

 described, to support a pouch, but to aid in the function of the mam- 

 mary glands and testes, they are, he adds, of course present in the 

 skeleton of these small pouchless Opossums, as in the more typical 

 Marsupials. [MABSUI-IATA.] 



The term Opossums is generally used to designate the Didelpkina, 

 now confined to the American continents. The former existence of 

 this type in Europe in association with Pal&ot/iertum, Anoplotherium, 

 and other extinct pachydermatous quadrupeds, is proved by the 

 fossil remains in the Paris Basin (Eocene of Lyell). Two species of 

 Didelphit have been found fossil in Great Britain. [MARSUPIATA.] 



The dentition of these scansorial Marsupials bears mre resem- 

 blance' to that of the Bandicoots (Peramelea) than to that of the 

 Darauri, if the structure of the molar teeth be excepted. 



The following species of this family are contained in the ' British 

 Museum Catalogue': 



li"l>Jphit Virginiana, the Opossum. North America. 



It. Aztirtr, Azara's Opossum. Brazil. 



Philander nudicaudui, Naked-Tailed Philander. Brazil. 



P. Opouum, the Philander. Tropical America. 



P. mariupialu, the Crab-Eater. Tropical America. 



P. dortigenu, Menair's Opossum. (See fig.). 

 HAT. HIST, BIV. VOL. it. 



P. cinemis, Cinereous Opossum. South America. 



P. murirmi, the Mamose. Tropical America. 



T/tylanus elegans, Elegant Painted Mamose. Chili, Valparaiso. 



(Owen, On /he Classification of the Marsnpialia, Zoo/. Trans, vol. ii.) 



Didelphis dursigera (Philander dorsiyenis, 'Brit. Mus. Cat.*). 

 From the specimen in the British Museum. 



DIDUS. [DODO.] 



DIDYMOPRIUM. [DESMIDIE*.] 



DIDYNA'MIA, the fourteenth class of the Linnsoan system of 

 arranging Plants. It is the same as Tetrandria ; that is, it has always 

 four stamens, only two of them are a little longer than the other two. 

 Under this class are comprehended a large part of the Lamiaceous, 

 Verbenaceous, Scrophalariaceous, Bignouiaceous, and Acanthaceous 

 Plants of modern botanists. It is divided into two orders, Gymno- 

 epermia and Angiospwmia. Gymnospermia includes the genera whose 

 ovary is split into four small seed-like lobes, which in the time of Lin- 

 naeus were taken for naked seeds ; and Angiospermia, those which have 

 manifestly the seeds inclosed in a pericarp of some sort. 



DIEFFENBA'CHIA, a genus of Plants belonging to the natural 

 order Araceie, to which the Caladium Seguinum, Dumb Cane, belongs. 

 [CALADIUM.] 



DIERVILLA, a genus of Plants belonging to the natural order 

 Caprifoliacece, consisting of a single North American species, by Lin- 

 naeus considered a honeysuckle, and called Lonicera, Dien'illa. It is 

 however obviously not of that genus, because its fruit is a dry capsule 

 with a papery pericarp, with four cells and several seeds. 



D. Tourneforti, or, as it is also called, D. humilis, D. lutea, or D. 

 Canadcnsu, is a common hardy shrub, growing from two to three feet 

 high, in a spreading manner, and having small funnel-shaped irregular 

 5-cleft yellow flowers, growing in stalked clusters of two or three 

 from the axils of opposite ovate serrated leaves. It is found wild in 

 rocky woods in the United States, from Canada to the Carolinas, 

 flowering in June. 



DIFFLUGIA. [INFUSORIA.] 



DIGENITE, a native Sulphuret of Copper. 



DIGESTION, the process by which the food is converted into 

 nutriment. Taken in its whole extent the process of digestion com- 

 prehends the entire series of changes by which the crude aliment is 

 assimilated into arterial blood. These changes are effected by organs 

 which, viewed collectively, comprise a most extensive apparatus com- 

 mencing at the mouth and ending at the lungs. 



The first changes upon the food are effected in the mouth, where it 

 is mixed with mucus and saliva. [SALIVA.] Torn to pieces by the 

 teeth [TEETH] in the operation of mastication, and softened by the 

 secretions of the mouth until it is reduced to a pulp, it is then col- 

 lected by the tongue [TONGUE], and formed by that organ into a mass 

 called a bolus. The bolus of food thus prepared is carried by the 

 tongue to a muscular membranous bag called the pharynx [PHARYNX], 

 situated at the back part of the throat. The pharynx, as soon as it 

 receives the bolus contracts firmly upon it, and by a proper muscular 

 action delivers it to the oesophagus, a long muscular tube which 

 extends from the pharynx to the stomach. [STOMACH.] The bolus of 

 food does not descend along the oesophagus by its own weight, for ;i, 

 person can swallow while standing on his head, and many animals 

 have obviously to convey their food along the oesophagus againsl 

 gravity. The food when it enters the oesophagus is transmitted along 



