220 BIOLOGICAL LECTURES. 



two fragments were united, if similar cells or cells destined to 

 form similar tissues were in juxtaposition, the tissues of the 

 more developed complex showed a perfect union across the 

 wound. This was the case with every kind of tissue except in 

 the notochord, where a break sometimes occurred at the line of 

 the wound. For example, in a belly to belly union the liver cells 

 of one tadpole being in contact with those of the other, a com- 

 mon liver would be formed in the older complex. The same 

 was true for the nerve cord where an anterior half of one 

 embryo was joined to a posterior half of another embryo, in 

 normal proportions; a complete spinal cord resulted. Where, 

 on the other hand, different kinds of cell masses were in con- 

 tact, only a connective-tissue union occurred ; when, for 

 instance, a head was fused to the belly of a complete tadpole, 

 its well-developed neural cord ended abruptly, although connec- 

 tive-tissue cells formed a connection with the tissues of the 

 major component. 



Owing to the interest aroused by Bern's results, the writer 

 endeavored to find another group of animals which would per- 

 mit of similar experimenting. Fortunately, the Lepidoptera 

 suggested themselves. Success was anticipated from the out- 

 set on general grounds, for the pupa of the Lepidoptera affords 

 an easily handled, quietly growing stage and one which pos- 

 sesses for the production of the imago within the pupal case 

 all the tissue-forming energy of an embryo. Furthermore, 

 beside the possibility of coalescence between two individuals 

 or parts of individuals, other very interesting lines of work 

 appeared ; namely, those bearing upon the production of the 

 often wonderful coloration of the wings. It had been shown 

 by the work of A. Mayer and others that the pigmental, as 

 opposed to the structural, colors in the wings of moths are 

 produced by the chemical decomposition of the haemolymph in 

 the empty scale cells. If, therefore, two pupae belonging to 

 differently colored species of moths could be made to grow 

 together and produce a pair of coalesced imagines, it would not 

 be unreasonable to expect from the mixed haemolymph at least 

 some sort of abnormal coloration, if, indeed, there did not appear 

 an actual color effect of each upon the other. Further support 



