

IV.] 'foundation of a theory of heredity. 227 



with staining reagents, while the other view, that it arises 

 from the cell-substance, is not based upon direct observation. 

 Consequently future investigation must decide whether the 

 paranucleus is to be considered as the spermogenetic nucleo- 

 plasm expelled from the nucleus. But even if this question is 

 answered in the affirmative, we should still have to explain 

 why this nuclear substance, remaining in the cell-body, does 

 not continue to exercise any control over the latter. 



Strasburger has recently enumerated a large number of 

 cases from different groups of plants, in which the maturation 

 of both male and female germ-cells is accompanied by pheno- 

 mena similar to the expulsion of polar bodies. In this respect 

 the phenomena occurring in the pollen-grains of Phanerogams 

 bear an astonishing resemblance to the maturation of the 

 animal ^.g^^. For instance, in the larch, the sperm-mother-cell 

 divides three times in succession, the products of division 

 being very unequal on each occasion ; and exactly as in the 

 case of polar bodies, the three small so-called vegetative cells 

 shrink rapidly after separation, and have no further physio- 

 logical value. According to Strasburger, the so-called ' ventral 

 canal-cell,' which, in mosses, ferns, and Conifers, separates 

 from the female germ-cell, reminds us, in every way, of the 

 polar bodies of animal eggs. Furthermore, the spermatozoids 

 in the mosses and vascular cryptogams throw off a small 

 vesicle before performing their functions ^ On the other hand 

 the equivalents of 'polar bodies' (the 'ventral canal-cells') are 

 said to be absent in the Cycads, although these are so nearly 

 allied to Conifers. Furthermore, ' no phenomenon occurs in 

 the oospheres (ova) of Angiosperms which can be compared 

 to the formation of polar bodies.' Strasburger therefore con- 

 cludes that the separation of certain parts from the germ-cells 

 is not in all cases necessary for maturation, and that such 

 phenomena are not fundamental, like those of fertilization, 

 which must always take place along the same morphological 

 lines. He further concludes that the former phenomena are only 

 necessary in the case of the germ-cells of certain organisms, 



\} It is almost certain that this vesicle is not derived from the nucleus, 

 but from the cytoplasm of the sperm-mother-cell. See Douglas H. 

 Campbell, ' Zur Entwicklungsgcschichte der Spermatozoiden' in Berichtc 

 der deutschen botanischen Gesellschaft, vol. v, 1887, p. 122.— S. S.] 



Q 2 



