Horváth Géza (szerk.): A Magyar Természettudományi Múzeum évkönyve 8. (Budapest 1910)

Soós, L.: A Helix arbustorum hím csirasejtjének fejlődése

312 LH L. SOÓS coalesce, and thus originate ringlike structures (Pl. VIII.

, Fig. 6.). But it would be an error to conclude the true structure from the appearence of the figures as it was done by BOLLES LEE. It is not to be forgotten that we see in such cases, as a rule, the optical sections of the chromosomes, the form of which varies naturally according to the direction of the cut; nor less important is the fact that we have not yet definite, but developing chromosomes before us. Their careful study shows they consist at this stage of a quite irregular groups of chromomeres. We can regard the chromosomes as definitely formed when their chromomeres melt together into a homogeneous mass, and their outlines become smooth and sharp. Their shape is even then irregular, spherical or polymorphic. They lie, as a rule, immediately under the nuclear membrane, to which they are very often attached (Pl. VIII., Fig. 9.). The number of the chromosomes is in this stage well countable, and we can determine that they are present in reduced numbers. The greatest number which I could accurately count was 21 ; the true number with the greatest probability is that found by the authors (PLATNER, BOLLES LEE, ANCEL) in the spermatocytes of Helix pomatia, i. e. 24. The chromosomes of Enteroxenos Östergreni, according to the researches of BONNEVIE (13, 14). develope in quite the same manner as those of H. arbustorum, but the nuclear membrane in Enteroxenos dissolves earlier, i. e. then, when the chromosomes are represented by irregular loose groups of chromomeres. Synchronously with the definite forming of the chromosomes appears also the centrosome which is to be found then in the cytoplasm close to the nuclear membrane (Pl. VIII., Figs. 7., 8.). The centrosome of H. pomatia, according to BOLLES LEE (10), first appears within the nucleus, and its presence can be determined before the definite formation of the chromosomes. It passes out of the nucleus only at the end of the prophase. Similar observation has been made by B

RAUER (17) in Ascaris megalocephala. I have not found any sign of its appearing within the nucleus though I worked also with BOLLES LEE'S methods. I was able to determine its presence with certainty when it was already lying in the cytoplasm, and was surrounded by astral rays. The centrosome is at that time very small, and consists only of the centriole, the centrosphere appearing later. The centriole soon divides — or perhaps it was even earlier double like in Ascaris according to 0. HERTWIG (48) — and the two corpuscles pass along the nuclear membrane toward the opposite poles of the cell (Pl. VIII., Fig. 8.). The nuclear membrane at the beginning of the metaphase disappears (Pl. IX., Fig. 5.), and the centrioles which have then also centro-