METHODS 23 



definite succession being evident. There is but little displacement of the 

 original division-walls, so that up to the last divison of the sperm-cells 

 the limits of the earlier divisions can be plainly traced, and the spermato- 

 cytes are in irregular blocks marking the early divisions. While within 

 these blocks of cells the nuclei are usually in the same stage of mitosis, 

 each segment of the antheridium may show a different stage of nuclear 

 division. This was also noted by Humphrey in his study of Fossombronia 

 longiseta [1]. 



Spermatogenesis 



Pallavicinia Zollingeri proved the best species for a study of sperma- 

 togenesis, and the investigation of this subject was mainly devoted to that 

 species. In the earliest stages procurable the final mitosis had taken 

 place, and the two resulting nuclei had begun to assume the elongated 

 form found in the completed spermatozoid (Fig. 12, A, B). The final 

 mitosis is accompanied by the formation of a delicate but perfectly evi- 

 dent division wall separating the pair of spermatocytes. The spermato- 

 cytes at this stage closely resemble those of Calycularia radiculosa (Camp- 

 bell [2], Fig. 7). The length of the young spermatocyte in P. Zollin- 

 geri is about J\i. Fig. 12, A, shows the pair of spermatocytes at this 

 stage. The blepharoplast (bl.) now has the form of a somewhat curved 

 rod at the end of the elongated nucleus. Sometimes the blepharoplasts 

 of the pair of spermatocytes are at the same end, sometimes at opposite 

 ends. With the development of the spermatozoid, the blepharoplast, as 

 usual, elongates rapidly, and becomes a slender curved rod, hooked at 

 the free apex, and following the curve of the elongating nucleus which 

 becomes crescent-shaped, with the anterior end more or less conspicuously 

 attenuated (Fig. 12, D-K). In some of the preparations there was pres- 

 ent between the blepharoplast and the anterior part of the sperm-nucleus 

 a thick, rod-shaped body, which perhaps represents the "Nebenkorper" 

 described by Ikeno [1] in Marchantia. The cilia arise from the ble- 

 pharoplast a short distance back of the apex, and become finally about as 

 long as the body of the free spermatozoid, which is about i6u. in length. 



The development of the spermatozoid in P. radiculosa was found to 

 be so much like that of P. Zollingeri that no attempt was made to follow 

 it in detail. However, some of the later stages in the last mitosis of the 

 spermatocyte, which were not seen in P. Zollingeri, were secured in P. 

 radiculosa. The nuclei are so small that difficulty was experienced 

 in determining the number of chromosomes, which is probably eight 

 ("see Fig. 12, N-Q). The spermatocytes are separated, as in P. 

 Zollingeri, by a delicate membrane, which is more difficult to demonstrate 



