ZooL.— Vol. II.] RITTER-CONGDON—STENOSTOMA. 37 1 



point, such cases as the grafting the cock's spur upon the 

 ox's ear, mentioned by Darwin, nor the union of the 

 posterior parts of two earth-worms to produce an animal 

 with a tail at each end recently accomplished by Joest (1897) 

 and by Morgan (1897). It should be borne in mind, however, 

 that these can hardly be regarded as trul}^ successful grafts; 

 i. e., they do not really get into the life cycle, reproduction 

 included, of the organism. In the case of the earth-worm, 

 for example, the success of the graft is local, so to speak; 

 i. e., it is successful, in all probability, only in respect to the 

 tissues that actually unite with one another, and can hardly 

 have much significance for the total life of an indi- 

 vidual earth-worm.^ With regard to the second point it is 

 only necessary to recall the fact that the question was long 

 in debate, if indeed it is fully settled yet, as to whether the 

 graft can exert any reciprocal influence at all upon the 

 stock. 



Another obvious difference between the " regulation " in 

 Stenostoma and that in the embryos referred to is in the fact 

 that in the first case the regulation begins with an adult, 

 and hence already differentiated, part, whereas in the second 

 it begins with wholly undifferentiated parts. Accepting the 

 idea of the equivalency of the blastomeres, the regulative 

 changes in Stenosto7na would seem to lie nearer the roots of 

 the morphogenic process here than in the embryos. They 

 are more comparable to the class of regulations of which the 

 production of new tentacles from the coenosarc in the 

 hydroides, as first observed by Miss Bickford (1894) is 

 a type. 



Still another difference is seen in the larger part which 

 external factors play in the embryonic than in the Stenos- 

 2fo/;z« regulation. The blastomeres are actually held to their 

 new position by external pressure, while there is no such 



1 From Joest's results it seems that at best the union of two posterior ends length- 

 ens the life of both pieces somewhat. The oldest worm of this kind reported by him 

 was eleven months and two days. Morgan found that the posterior, unregenerable ends 

 would heal the wound and live for four months at least. It would be interesting to 

 know whether united pieces of this kind would live longer under precisely the same 

 external conditions than ununited pieces of the same number of somites. 



