222 PROCEEDINGS OF THE ACADEMY OF [April, 



characteristics of color and consistency are fouud to be of small 

 value. Number is iu strict sense not a characteristic of an 

 organ, but duplication of organs is a characteristic of the general 

 plan, as in bilaterally symmetrical forms where certain organs 

 are paired, in metameric forms where they are serially duplicated, 

 in radiate forms where they are antimerically duplicated. Some- 

 tmies an organ is excessively duplicated without any corresponding 

 duplication of the body plan (e. g., testes within one proglottid of 

 a Cestode). The relation that the number bears to the larger 

 divisions of the organization must be determined, in order for us 

 to conclude whether the two correspond; for when number of 

 organs and number of larger body parts correspond, the number 

 would have more significauce for the comprehension of the whole 

 organization than if there were no such correspondence. IS^umber 

 is a characteristic which must always be carefully considered, for 

 the relative degrees of duplication of organs and of their concentra- 

 tion or concrescence are of great importance iu estimating the 

 affinity of the organism to its allies. 



The position of an organ with I'egard to the other organs is also 

 a characteristic to be carefully considered, though perhaps it has 

 not the same value as number ; thus whether the central nervous 

 system lies above or below the intestine or heart, and whether the 

 skeleton is external or internal. For if variations in the position 

 of an organ cannot be readily explained by change in mode of 

 life, it is probably the case that more conservative intrinsic growth 

 energies are the occasion, and the latter should be ascribed great 

 importance until the contrary be proved. It is just these phe- 

 nomena, which seem most inexplicable, that should serve as warning 

 signals not to proceed further until many explanations for them 

 have been tested. Why the genital orifices iu certain Rhabdocoelida 

 are near the anterior end, in others near the posterior end of the 

 body, we do not yet understand, and it is very difficult to give a 

 good reason for the shifting of such important structures. But 

 until it is proved that the shifting is due to some trivial cause, we 

 have no right to disregard in classification such differences of posi- 

 tion. Again, such an apparently trivial characteristic as the posi- 

 tion of the anus : in most freely motile Metazoa it is ventral, in 

 the Entomostraca and the Rotatoi'ia it is dorsal. The dorsal position 

 in these two groups has been given no particular morphological 



