The anatomy of symmetrical double monstrosities in the trout

This paper contains the results of an investigation into the anatomy of a series of trout embryos exhibiting different degrees of symmetrical duplicity, and gives an account of the structural details which attend the fusion, disappearance, or special adaptation of parts in the region of transition from the double to the single condition. Some general questions suggested by these results are also discussed. The monstrosities examined were four months old counting from the time of fertilisation, and they form a fairly complete series ranging from specimens in which the duplicity does not affect more than the anterior part of the head to specimens in which there is union by the posterior part of the body or by the yolk-sac only.