No. 419.] ONISCUS ASELLUS LINN. 923 
double row of four granules. After division the halves con- 
sist of a double row of two granules, or four in all, and thus 
simulate tetrads. 
The true nature of the second maturation division, whether 
equational or reductional, is difficult to decide, because the 
length and the breadth of the chromosomes are 
approximately equal. Since most writers on the 
€» maturation of the germ cells in the arthropods 
agree in ascribing to them both methods of 
Fic.s.—Equatorial division (equation and reduction), it is probable 
owl cane that since the first division is reducing, the second 
is equational in Oniscus. 
These results do not agree with those obtained by Rückert ! 
and vom Rath? in the ovogenesis of the copepods. The case 
of Cyclops.as described by Riickert is partic- ne 
ularly clear. According to his observations 
the first maturation division is equational, 
the second reducing. If Rückert's inter- 
pretation of the method of reduction in 
Cyclops be correct, and my own concerning 
reduction in Oniscus be equally so, it be- 
comes clear that the cell generation in which 
the true reduction takes place need not be 
the same for all members of a given class of 
animals. 
2. Metamorphosis of the Spermatids. 
The transformation of the spermatids of 
the isopods has already been described by 
Gilson? in his comprehensive work on the 
lRückert, J. Die Chromatinreduktion der C 
hromo- Fic. 6 — Anterior portion 
somenzahl im Entwicklungsgang der Organismen, o 
Merk. of mature sperm colony 
y magnified). 
u. Bon. Erg., Bd. iii, 1893. Jf. flagellum j jar Pre" 
Id. Zur Eireifung bei Copepoden, Merk. u. Bon. ETS. in me spa: n 
A $ SSe N 
nat. Heft, 1894. Chroma- of cytoplasmic fibres. 
2Vom Rath, O. Neue Beiträge zur Frage der j 
tinreduktion in der Samen- und Eireife, 4. M. A., 46, 1895. 
3 Gilson G. Spermatogénèse chez les podes, 
1886, tomes i and ii. 
La Cellule, 1884 and 
