43 2 Moore. — Essential Similarity of Chromosome 
thing like so certain as Dr. Haecker’s statements would lead 
one to suppose. In fact, when the whole of the current observa- 
tions relative to the maturation of the sexual elements of 
animals are taken into account, it is quite clear that Dr. Haecker 
speaks more or less entirely for himself and the supporters 
of the particular theory of heredity which he adopts. 
This is rendered the more obvious from the contents of 
the foot-note on page 99, in which he says that ‘ there is at the 
present day only one observation which directly opposes this 
generalization (the universality of the ‘ Reductionstheilung ’). 
Compare Brauer, Archiv fur Mikr. Anat., V, 42, 1893, although 
I had, as a matter of fact, previously published accounts of the 
maturation of the male sexual element in Mammals 1 and 
Elasmobranchs 2 , which, in agreeing with the corresponding 
processes of plants, were quite as much opposed to the 
hypothesis in question as any observations made by Brauer. 
The conception of a 4 Reductionstheilung’ is claimed as 
a necessary consequence arising from the premises of Weis- 
mann’s theory of Heredity, and is defined as a division in 
which half the nuclear elements, idants, or chromosomes, pass 
unsplit into each daughter-cell. As Weismann 3 says — 4 the 
reducing division does not consist in the idants becoming 
split longitudinally, and in their resulting halves being 
1 Mammalian spermatogenesis, Anat. Anz. VIII, 1893, p. 683. In this paper 
the course of the spermatogenesis was summarized as follows : 1 There is in the Rat, 
(1) a period of indifferent cell-formation, terminated by a mitosis with apparently 
sixteen chromosomes both in the primary and daughter-cells ; (2) a period of 
growth, during which the sixteen elements are converted into eight, and terminated 
by a mitosis in which the daughter-nuclei still retain the number eight ; (3) a period 
during which the spermatids are converted into spermatozoa/ There is obviously 
no ‘ Reductionstheilung,’ but the process of maturation of the sexual cells is 
exactly comparable to that which occurs among the higher plants. 
2 On the germinal Blastema, and the nature of the ‘ so-called ’ reduction division 
in the cartilaginous fishes, Anat. Anzeig. IX, 1894, p. 548. In this paper I fell 
into the error of supposing that a reduction occurred in the rest between the two 
last divisions ; this is not the case, and my mistake was due to -want of optical 
power and successful preservation. With this correction the spermatogenesis of 
Elasmobranchs is exactly comparable to that of mammals, except that two 
generations follow the great spermatic heterotype, instead of one. The last division 
is a heterotypic one. 
3 The Germ-plasm, Parker’s translation, p. 236. 
