II MUSCINE^— HEPATIC^— MARCHANTIALES 17 



Later, by a series of periclinal walls, a central group of cells is 

 separated from an outer single layer of cells. The latter divide 

 only a few times, and develop chlorophyll, which sometimes 

 changes into a red or yellow pigment at maturity. The inner 

 cells give rise to a very large number of sperm cells, which in 

 most Hepaticae are extremely small, and consequently not well 

 adapted to studying the development of the spermatozoids. In 

 a few forms, however, they are larger ; and in Pellia especially, 

 where the sperm cells are relatively large, the development has 

 been carefully studied by Guignard ( i ) , Buchtien ( i ) , and 

 others of late years, as well as by many of the earlier observers, 

 and a comparison with other Hepaticae shows great uniformity 

 in regard to the origin and development of the spermatozoid. 

 After the last division of the central cells the nuclei retain their 

 flattened form, and thus the sperm cells or spermatids remain 

 in pairs, an appearance very common in the ripe antheridium 

 of most Liverworts. Just before the differentiation of the 

 body of the spermatozoid begins, the nucleus has the appearance 

 of an ordinary resting nucleus, but no nucleolus can be 

 seen. The first change is an indentation in the edge of the 

 discoid nucleus, and this deepens rapidly until the nucleus 

 assumes a crescent form. One of the ends is somewhat sharper 

 and more slender than the other, and this constitutes the 

 anterior end. As the body of the spermatozoid grows in 

 length it becomes more and more homogeneous, the separate 

 chromosomes apparently fusing together as the body develops. 

 The body of the spermatozoid increases in length until it forms 

 a slender spiral band coiled in a single plane, lying parallel with 

 the one in its sister cell. The full-grown spermatozoid in 

 Pellia epiphylla has, according to Guignard ((i), p. 67) from 

 three to four complete coils. Usually when the spermatozoid 

 escapes, it has attached to the coil a small vesicle which swells 

 up more or less by the absorption of water. This vesicle is 

 the remains of the cytoplasm of the cell, and may, perhaps, 

 contain also some of the central part of the nucleus. Gui- 

 gnard ( (i), p. 66) asserts that sometimes the cytoplasm is all 

 used up during the growth of the spermatozoid, and that the 

 free spermatozoid shows no trace of a vesicle. 



In the Ricciaceae and in Sphcsrocarpiis new archegonia 

 continue to form even after several have been fertilised, so that 

 numerous sporogonia develop upon the same branch of the 

 2 



