Some Problems of Reproduction: a Comparative Study of ...

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SOME PROBLEMS OP REPRODUCTION. 57 advance, are only evenly distributed between the daughtercells. This obviously, as stated, is only another way of distributing the segments formed. If in the schema B, C, represent two of the chromatomeres of the gametogonial nucleus, B 1 , C 1 —B 2 , C 2 , those produced by their splitting, and the dotted lines the cell divisions, we see that the sole difference needed to change this into a schema of ordinary cell division would be to prolong the middle dotted line back to the level of B 1 , C 1 —B\ C 1 . /B a , C 3
58 • MARCUS M. HARTOG. asexual spores in Archegoniate Cryptogams. Hence we may be allowed to conjecture that the reduction also takes place in the latter group ; and, by parity, that it is not confined to gametogonia, but will be found in all mothercells destined by multiple fission to give birth to a brood of reproductive cells. In that case the return to the normal number of chromatomeres would necessarily be effected by the slow process of nutrition in asexual spores or their offspring, instead of by the direct process of summation in the case of gametes. This would give a clear insight into the action of karyogamy in bringing about rapid and complete rejuvenescence. The question of the individuality of the chromatomeres and their persist, ence, as maintained by Boveri and Rabl, should find its treatment here ; but I have not yet completed a research bearing on this point. I therefore confine myself now to the statement that, with Hertwig, I believe the evidence very inadequate for the support of the theory that the chromatomeres have distinct and persistent individualities. Professor Strasbiirger has written me a letter to the same effect, though he had advocated Rabl's views in his ' Kern- und Zelltheilung.' B. On the Reproductive Incapacity of Obligatory Gametes. The reproductive incapacity of gametes is no exceptional phenomenon among cells, nor is it brought about only in the differentiation of gametes. It occurs in other cases throughout the Metaphytes and Metazoa, and we have instances of its existence as low down as the Colonial Flagellates. In the genus Volvox all the numerous cells of the colony other than the few ''germinal cells" (parthenogonidia, oogonia, or spermatogonia), perfect flagellates equipped with eye-spot, contractile vacuoles, and nucleus : all these, I say, are affected by that very reproductive incapacity which is the character, istic of the gametes, while they lack the potentiality of karyogamic rejuvenescence possessed by the latter. In the majority of Metazoa and Metaphytes the tissue-cells as a rule suffer from the same impotence in virtue of their differ-
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Some Problems of Reproduction: a Co
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SOME PROBLEMS OP REPRODUCTION. B. T
Page 5 and 6:
4 MABCUS M. HARTOG. of gametes by r
Page 7 and 8: 6 MARCUS M. HARTOG. MEMOIRS— "Sur
Page 9 and 10: 8 MARCUS M. HARTOG. also of karyoga
Page 11 and 12: 10 MARCUS M. HARTOG. Among the mari
Page 13 and 14: 12 MARCUS M. HARTOG. Chlamydomonas
Page 15 and 16: 14 MAKO[JS M. HAETOG. (Epithemia, A
Page 17 and 18: 16 MAECUS M. HARTOG. COLEOCHJETE^:
Page 19 and 20: 18 MARCUS M. HARTOG. indicating the
Page 21 and 22: 20 MARCUS M. HABTOG. VAUCHERIA is c
Page 23 and 24: 22 MARCUS M. HABTOG. The last two g
Page 25 and 26: 24 MARCUS M. HARTOG. mantle around
Page 27 and 28: 26 MARCUS M. HAETOG. Saprolegniese
Page 29 and 30: 28 MARCUS M. HARTOG. by the nuclei
Page 31 and 32: 30 MARCUS M. HAETOG. The BANGIACE-E
Page 33 and 34: 32 MARCUS M. HARTOG. 2. Characese.
Page 35 and 36: 34 MARCTTS M. HAETOG. in the great
Page 37 and 38: 36 MAEOUS M. HARTOGt. 2. Angiosperm
Page 39 and 40: 38 MAROUS M. HARTOG. mation of thes
Page 41 and 42: 40 MARCUS M. HAETOO. divisions of t
Page 43 and 44: 42 MAROUS M. HARTOG. of further vit
Page 45 and 46: 44 MARCUS M. HAKTOG. view is that i
Page 47 and 48: 46 MARCUS M. HARTOG. The following
Page 49 and 50: 48 MARCUS M. flARTOG. This confirms
Page 51 and 52: 50 MARCUS M. HARTOG. matogenygoes o
Page 53 and 54: 52 MAROtJS M. HAKTOG. In the presen
Page 55 and 56: 54 . MAEOTJS M. HAE.TOG. Though we
Page 57: 56 MAROUS M. BARTOG. meres in the v
Page 61 and 62: 60 . MABCTJS M. HABTOG. nay, in som
Page 63 and 64: 62 . MARCUS M. HAHTOG. either direc
Page 65 and 66: 64 MAUCtJS M. HATJl'OG. We see that
Page 67 and 68: 66 MARCUS M. HARTOG. Parallel cases
Page 69 and 70: 68 MAECUS M. HAETOG. ciated, may oc
Page 71 and 72: 70 MARCUS M. HAETOG. superBuities
Page 73 and 74: 72 MARCUS M. HABTOG. D. THE ORIGIN
Page 75 and 76: 74 MARCUS M. HARTOG. zygote in the
Page 77 and 78: 76 MABCUS M. HAETOG. 4. Isogamy, pl
Page 79 and 80: 78 MABCUS M. HARTOG. heteroecism) i
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