INTRODUCTION There is a reciprocal relationship between tu mor agents and cellular differentiation. A particu lar agent may be introduced into only one type of differentiated or partially differentiated tissue. At the same time, an agent from a donor neoplasm will, when introduced into cells of a new host, not only induce rapid growth but also cause the host cells to become identical in appeara...

1. A maximum of 15 loci from five genera of caecilians (Amphibia: Gymnophiona or Apoda) were examined. Species include lchthyophis glutinosus, Geotrypetes seraphini, Caecilia occidentalis, Gymnopis multiplicata, and Dermophis mexicanus. 2. The data indicate that [chtkyophis (family Ichthyophiidae) is less closely related than are the other genera (members of the family Caeciliidae). Dermophis a...