2 7 o NOTES AND COMMENTS [apeil 



smooth skate {liaia batis) leucocytes appear at a time when the spleen 

 has no existence, when there is no rectal gland nor lymphoid structures 

 of any sort. The leucocytes are then present in the epithelial cells of 

 the thymus primordia. Thence they soon begin to migrate, emerging 

 in crowds which cause larger or smaller " breaks " at various places on 

 the contour of the thymus. As the author puts it : — " It is Kolliker's 

 great service to have shown that leucocytes arise in the thymus from 

 its original epithelial cells ; to Gulland's researches we owe the result 

 that the first leucocytes are found in the mesoblast in the neighbour- 

 hood of the thymus; and, finally, it has fallen to my lot to show that 

 the first leucocytes arise in the thymus from its epithelial cells, and 

 that thus it is the parent source of the leucocytes of the body." We 

 are not clear as to the logic of the " thus " in the last sentence, but the 

 discovery is a triumph, and we eagerly look for a full paper with 

 illustrative figures. 



Antlierozoids in Gymnosperms. 



The long-expected account of antherozoid formation in Cycas revoluta 

 has at length appeared in a form which renders the extremely valuable 

 results obtained by Mr. S. Ikeno available in all their details to the 

 ordinary European reader (Jahrb. f. wiss. Bot. Bd. xxxii. 1898). Several 

 notices which have from time to time appeared in various publications 

 have already made us acquainted with the general outline of the 

 research, but we have now before us for the first time a complete 

 account of the process of fertilisation in Cycas as it takes place under 

 normal conditions in the natural habitat of the plant. 



The development of the archegonium differs but little from that in 

 other Gymnosperms, except as regards the enormous size, 4 mm. x 1 mm., 

 reached by the adult organ. The most remarkable results obtained are, 

 however, those relating to the germination of the pollen grain, a pro- 

 cess for the completion of which a period of three months is required. 



The greater part of the ripe spore is composed of a large round 

 " embryonal " cell, accompanied by two much smaller " germinal " cells 

 placed one above the other close against the inner side of the wall. 

 The pollen tube arises in the usual way from a thin area in the wall 

 of the embryonal cell, the nucleus of which accompanies the apex of 

 the tube as it bores its way into the nucellar tissue, where it branches 

 and apparently soon becomes quiescent. Meanwhile the two germinal 

 cells have become spherical, at the same time increasing considerably 

 in size, especially the inner one, the nucleus of which divides in a 

 direction at right angles to the axis of the pollen tube, without how- 

 ever any formation of a cell wall. One of the resulting daughter 

 nuclei commences to grow rapidly while the other remains of small size, 

 and is ultimately crushed against the wall by its more successful sister. 



