We have here a great variety of malformations according to the degree of defect of the smaller portion. The fully-developed foetus is continuous with the head, while the imperfect one seems a mere appendage, or is even broken off from the former. We are able to recognize various modifications.

(A) Acephalic Parasites (Smaller Part Appended To Front Of Larger)

In this form we have the fully-developed foetus with part of an ill-developed one hanging from the front of the thorax and abdomen in the form of two legs, or two legs with part of a body and two arms. This form is sometimes called Epigastrius. It is the commonest form of the parasitic monstrosities, and is illustrated in the case of a Hindu youth, called Lalloo.

(B) Inclusio Fcetalis, Foetus In Fcetu (Smaller Part Included In The Other)

The included portion is within the abdominal cavity of the larger part (Engastrius), and is very ill developed. It lies in a sac composed of connective tissue, and the parts are rather confusedly mixed, but there are usually recognizable the bones of legs and arms with hands and feet - sometimes also portions of the vertebral column.

Some cases of Congenital sacral teratoma are to be included in this group, those namely in which the tumour contains well defined parts of the foetus, such as recognizable bones of the skeleton, etc. See further under Tumours in the class of Teratoma.