HADRIAN. 435 HAECKEL. in width, with a single archway 20 feet wide, surmounted by an attic with three openings. The inscriptions fronting the new and the old city are still in place. HADBIAN, Tomb or JIausoleum of (Lat. Hadrianunt) . The massive building in Rome now known as the Castel Sant' Angclo. It was erected in a.u. I'Sii by the Emperor Hadrian, to- gether with the J<jlian 15ridge (Ponte Sant' An- gelo), which gave access to it. The tomb was situated in the gardens of Domitia, on the bank of the Tiber. It consisted of a ba.sement 247 feet sqiuire. surmounted by a circular mass of masonry 230 feet in diameter, both faced with Parian marble. The whole was crowned with a cone of earth planted with evergreens. The tomb was adorned with statues and surrounded by a gilt bronze railing with gilt peacocks, two of which are preserved in the Vatican gardens. The front of the basement had panels bearing the names of the members of the Imperial family buried in the tomb. The entrance to the burial- chamlier was in the front, facing the bridge. The structure was fortified in the time of Honorius, and was the centre of the factional strife dur- ing the mediteval and modern history of Rome. The castle was held by the popes from the time of Boniface IX.. and about 1500 was connected with the Vatican by a subterranean passage. The ancient structure is almost concealed l)y the works of fortification which have been added to it, and has been despoiled at various times. The marble tombstones were used by Gregory XIII. in the construction of his Gregorian Cliapel in the Vatican, and the mausoleum supplied the materials with which the Sistine Chapel was built. The gilt angel sheathing his sword, and with outstretched wings, on the pinnacle of the struc- ture, is a modern work, taking the place of previ- ous statues destroyed or stolen during the ilid- dle Ages. It commemorates the appearance of the Archangel Michael to Gregory the Great dur- ing a plague. HADRIAN'S VrLLA. A magnificent coun- try place laid out and built by the Emperor Ha- drian near Tibur (Tivoli). It covered an area of several .square miles, and its different parts bore the names of famous scenes and buildings which Hadrian had visited in his travels. It contained gardens, theatres, a stadium, apartments, baths, colonnades, terraces, and many artificial land- scafie features, carried out with lavish use of costly materials, which were subsequently used in the construction of other buildings. The ruins, in great part preserved, have for centuries yielded important works of ancient art, now in the vari- ous museums of Rome. HADRIAN'S WALL, See Roman Wall. HADROME, had'rAm (from Gk. rirSpof, hadros, thick). The conducting portion of the woody part of a vascular bundle. It includes the ves- sels, traeheids. and wood parenchyma, but not the libriform cells. Where the libriform cells are lacking altogether, as is generally the case in monocotyledons, the hadrome and xylem are identical. See Leptome and Mestojie. HAD'ROSAU'RUS (Neo-Lat., from Gk.nfVoc, hadros. thick + anvpocsntii-os, lizard). A gigan- tic fossil lizard of the dinosaur group, found in (he Cretaceous sandstones of Wyoming. The shape of the animal was very peculiar. With a length of 35 feetj it had a small head, short fee- bly built fore legs and strong hind limbs, and heavy tail. Its jaws were broadened laterally to form a fiattened bill like that of a duck. Portions of thick rhinoceros-like hide were found asso- ciated with the skeleton. The animal is consid- ered to have been an amphibian, feeding on succulent marsh plants, for which habit its flat- tened beak seems to have been j)eculiarly adapted. See DijSosalhia. HADRUMETUM ( Lat., from Gk. 'A^pov- fi'lTi'l', IJarlroiiiiiclos) . An ancient city on the Af- rican coast of the Mediterranean on "the Gulf of Hammamet (Tunis). A PlKcnician colony which claimed to be of earlier date than Carthage, in ctairse of time it became subsen-ient to the Impe- lial city, and fell along with it under the power of the Romans, On the subdivision of the Ro- man Province of Africa Propria, it became the capit;il of Byzacium. By Trajan it was made a colony — Colunia Concordia XJlpia Traiana Au- f/iista Fniiiifcra Hadruinetina. From the devas- tation indicted by the Vandals, it was restored by Justinian, and in consequence it bore for some time the name of Justinianopolis. It is now called Susa. HAECKEL, hek'l, Ernst (1834—). A Ger- man zoiilngist and natural philosopher, born at Potsdam. He studied medicine and the nat- ural sciences at Berlin, under .lohannes Miiller, and at Jena. After taking his medical degree at Berlin, he practiced medicine for a year, and then, having decided to devote himself to the nat- ural sciences, he studied marine life in Heligo- land, Messina, and Naples. In 1861 he became privat-docent, in 1862 professor extraordinarius, and in 1865 professor of zoiilogj- at Jena. He made numerovis scientific journeys, to the Canary Islands, to Norway, the Adriatic, the Red Sea, Corsica, Sardinia, Ceylon, and Java. He pub- lished: Die Radiolarien (1862) ; Die Hydromedu- sen (1865) ; Entwicklunnsyeschichte der Hiphono- phoren (1869); iloneren ttnd andere Protisten (1870); Die Kalkschmimmc (1872). The last named work is an impoitant monograph upon calcareous sponges, in which an attempt is made to arrange them in a natural system; the prop- osition being that tlie layers forming the body- wall are also homologized with the ectoderm and endoderm of tlu' gastrula. This is the basis laid for the celebrated gastraea theory. Other in- vestigations are: Arabische Korallen (1876); Dn,s Hy stent der Medusen (1880-81) ; Reports on the h'adiolaria ; on the Deep Sea Medusa': on the Deep Sea Keratosa : on the fiiphonophora Col- Jectcd h;i the ChaUenficr (1882-88); Plankton- Stiidien (1890), Haeekel's philosophical writings were first inspired by Darwin's Origin of Species. In 1866 appeared Die ficjicrelle Morplmlnriie der Orfjanisnicn, which was the first attempt to apply the general doctrine of development to the whole field of morphology', and also to found a classifi- cation of animals and plants based ujjon the doc- trine of their common relationship. In it he formulates tlie celebrated 'biogenetic' law, al- ready stated by Von Baer, Agassiz. and Fritz Mviller. In 1868 appeared Xotiirliche Schopftinijs- (leschichte. translated into English as the TJis- torii of Creation, which is a popular exposition of ihc doctrine of evolution, and has had the widest circulation and done more to popularize Darwin- ism in Germany than anv other hook. Feher die Entstehung und den Siammbaum des Merv-
