524 CLARENCE E. McCLUNG 



of the spermatogonium — the member which was added during 

 synapsis having been removed in the first spermatocyte mitosis. 

 The second spermatocytes are accordingly of the usual di- 

 morphic character, one with the accessory chromosome — here 

 permanently joined to a euchromosome — and the other without 

 it. Since the V is made up of a dyad plus the accessory chromo- 

 some dyad, it is, in effect, a tetrad, but of unusual type since 

 its parts are not homologous. It divides here just as do tetrads 

 in the first spermatocyte, and the anaphase shows a V going to 

 each pole along with the ten rods. The union of the accessory 

 chromosome with one euchromosome is therefore not lost dur- 

 ing all the changes of the maturation period, but persists into 

 the spermatozoon and, by it, may be handed on to the female 

 line of the next generation from which it passes into the male 

 line upon the following fertilization. 



3. The complex of H. pratensis 



In this species, as in H. speciosus, there is uniformly present 

 a multiple chromosome which differs from the speciosus form 

 only in the proportion of its parts. Without some more defi- 

 nite criterion for the homology of the euchromosomes than we 

 now possess it is not possible to say that it is the same mem- 

 ber of the complex with which the accessory chromosome unites 

 in the two species. If size only were used as a basis for judg- 

 ment, then it would be necessary to say that different tetrads 

 are involved, because the euchromosomes are much larger in 

 speciosus than in pratensis. From the fact that the accessory 

 chromosome itself may vary considerably in different species, it 

 would appear that size is not alone a safe indication of homology. 

 Leaving out of consideration the question of whether it is a 

 particular one of the eleven tetrads with which the accessory is 

 joined, we face the concrete fact that so far as our observations 

 have gone, there is always such a multiple element present in 

 the germ cells of the two species. 



AVhen we come to observe the character of the multiple ele- 

 ment in the different generations of cells it is found to exhibit 



