PRODUCTION OF MONSTERS BY HYBRIDIZATION. 317 



(B) FORMS RESULTING FROM DIFFERENTIAL ACCLIMATION OR 



RECOVERY. 



Of somewhat less frequent occurrence than the above described 

 types of fish hybrid teratomata are those in which the apical and 

 mesial parts have become acclimated to (or adjusted to) the 

 materials brought in by the foreign sperm. The less extreme 

 types are those in which the head is relatively large and wide as 

 compared with the trunk and tail. Next comes a whole series 

 of types in which first the tail and then the trunk are inhibited 

 more or less completely, and even heads without trunks but with 

 beating hearts are common. The most extreme cases are those 

 in which isolated eyes or isolated hearts grow upon an otherwise 

 undifferentiated blastoderm (Fig. 14). I have found several 

 examples of isolated eyes that could be distinguished only by the 

 presence of a lens and of pigmented retinal cells. Also isolated 

 hearts may be reduced to small pulsating "drums" of tissue in 

 which there is no axiate elongation. According to the axial 

 gradient theory not only are the apical points most susceptible 

 to inhibitors, but under certain circumstances, such as long 

 exposure to low concentrations, they have the highest capacity 

 for recovery. That is why eyes and hearts, the apical parts of 

 the two axiate systems, show the highest capacity for recovery 

 and are sometimes the only parts that do recover after long and 

 general inhibition. A very common type of teratomata is one 

 in which the whole body is decidedly abnormal, inhibited no 

 doubt at an early stage, but in which recovery of the apical 

 structures has occurred to various degrees, so that we have 

 forms in which the only highly differentiated parts are apical 

 parts. Such embryos are shown in Figs. 13 and 14. 



Child ('16) distinguishes between forms resulting from dif- 

 ferential acclimation, forms resulting from differential recovery, 

 and forms resulting from differential inhibition with general 

 recovery. While I believe that the forms resulting from hybrid- 

 ization are identical to those produced by chemical inhibition, 

 I am not able to say in any particular case whether a form is one 

 or the other of these three types. My judgment is that the 

 isolated eyes and hearts are -forms resulting from differential 

 recovery and that the forms with comparatively well developed 



