NEW TYPES OF CHROMOSOME DISTRIBUTION. 137 



phasizes the necessity of keeping all specimens for future identi- 

 fication. It seems very probable that the species which Mont- 

 gomery called "Sinea diadema" was Acholla nmltispinosa, for 

 the first maturation division in Acholla nmltispinosa agrees ex- 

 actly with that which Montgomery figured for Sinea. 



The behavior of the chromosomes in Sinea is practically the 

 same as in Prionidus and gives a beautiful confirmation of the 

 results there described. In the female cell (Fig. 6, A and B), 

 30 chromosomes are distinctly visible, six of which are much 

 smaller than the others. The male cells (Fig. 6, C and D) show 

 28 chromosomes, two less than the female number and four of 

 these are smaller than the rest. There are 16 chromosomes in 

 the metaphase of the first maturation division (Fig. 6, E and F], 

 and since there are 28 chromosomes in the spermatogonia, 12 of 

 these must be bivalent and four univalent. All the chromo- 

 somes divide equally in the first division. Hence the equa- 

 torial plate of the second division shows 16 chromosomes, 

 but as usual, their arrangement is different. In the first 

 division, the small chromosomes are peripheral, while in the 

 second, they are central and are arranged in a tetrad-group, 

 as are the four differential chromosomes in Prionidus. Fig. 

 6, / and J, show two side views of the second division, meta- 

 phase, with the tetrad group in the middle. In Prionidus, one 

 chromosome of the tetrad group is larger than the other three, 

 while in Sinea all four are practically the same size. In the 

 second division, the chromosomes in the ring divide, while the 

 tetrad group separates so that the three chromosomes above go 

 to one pole and the one below to the other. Fig. 6, K and L, 

 are two anaphases, showing the manner of separation. Two 

 classes of spermatozoa are thus formed, containing 13 and 15 

 chromosomes, respectively. Judging from these facts, the re- 

 duced female group contains 15 chromosomes and females are 

 produced upon fertilization by the i5-chromosome class of sper- 

 matozoa; males by the 13-chromosome class. 



Egg 15 plus spermatozoon 13 = 28 

 Egg 15 plus spermatozoon 15 = 30 



The size relations of the differential chromosomes which make 



