There is a genus, the _Rachipagus_, the examples of which are joined behind like the class Terata Anakatadidyma that are joined in front. {85} Four known attempts have been made to separate double monsters surgically, but all failed owing to crude surgery; modern methods might be successful in some cases. The second order of double monsters comprises the parasitic class. There are three genera of these terata, with five species and seventeen varieties. The chief of these only will be mentioned. The _Heterotypus_ is a parasitic child which hangs from the abdominal wall of the principal subject. Varieties of this species are the _Heteropagus_, which is a parasite with head and arms; the _Heterodelphus_, which has no head; the _Heterodymus_, which has a head, neck, and thorax. The _Heteralitis_ is a second species, in which the parasite is inserted at a distance from the navel of the autosite. The _Epicomus_ is the only example, and it consists of a parasitic supernumerary head. The _Polypnathus_ is a parasite attached to the jaw of the autosite. When fastened to the upper jaw, it is an _Epignathus_; at the lower jaw it is an _Hypognathns_. Another group is made up of terata having parasitic legs which are attached to different parts of the autosite,--to the pelvis, the head, the abdomen, and so on. Finally, there is the _Endocyma_, which is a parasite enclosed within the body of an autosite. Parasites are nourished through the blood supply of the autosite, and the parasites usually are incapable of motion. The autosite can feel when the parasite is touched, and in some cases the autosite can localise the touch. In India, in 1783, a child was born which had a supernumerary head attached to the autositic head, crown to crown; it lived four years. The parasite's eyes were always partly open, but they appeared to be incapable of intelligent vision. They contracted under strong light, and when the autosite was suddenly awakened both sets of eyes moved. Gould and Pyle (_Anomalies and Curiosities of Medicine_) give an account of an Italian boy, aged eight years, who had a small parasitic head protruding from near the left third rib. Sensibility was common. Each of the heads received baptism (one was called John and the other Matthew), and there was question as to whether extreme unction should be administered to the parasitic head. A similar case occurred in {86} England in 1880 (_British Med. Journal_), and the parasitic head could be pinched without attracting the attention of the autosite. Teratologists now exclude Dermoid Cysts from the lists of terata. The hair, teeth, and particles of bone found in these cysts are looked upon as the development of abnormal ectodermic and endodermic cells, rather than as evidence of a separate personality. There is only one well-authenticated case of a triple monster, and this happened in Italy in 1831. The monster had a single broad body with three distinct heads and two necks. It was killed in delivery.