i9i 2] CLAPP—ANEURA PINGUIS 181 



primary segment by a vertical transverse and horizontal wall, 

 which produces it. 



Sex organs 



Antheridia. — The antheridia of Aneura pinguis are borne in 

 the upper surface of lateral branches which occur singly, in groups 

 of three, or occasionally in groups of two. On the branch their 

 arrangement is extremely regular, in two alternating rows corre- 

 sponding to the segments of the apical cell. They appear imbedded 

 because of the rapid marginal growth of the surrounding cells. 



Leitgeb's diagram for their arrangement in Aneura palmata 

 holds true also for Aneura pinguis. After the division of the 

 primary segment into an outer marginal and an inner posterior cell - 

 by a vertical transverse wall, and after horizontal cleavage of the 

 latter into a dorsal and a ventral cell, the dorsal cell by a vertical 

 longitudinal division forms an inner (toward the median axis of the 

 thallus) and an outer (toward the lateral margin) cell. The inner 

 by a transverse vertical cut divides into two cells, the anterior of 

 which gives rise to the antheridium. This dorsal superficial cell 

 (the antheridium initial), containing a large nucleus and abundant 

 cytoplasm, enlarges and projects (fig. 16). It divides into two 

 cells, the outer of which, by a horizontal wall, forms a stalk cell 

 usually dividing once at least, and the antheridium mother cell (fig. 



17). 



The method of development follows the Jungermannia type. 

 First a vertical wall divides the outer cell into two equal halves (fig. 

 18). By two vertical intersecting walls in each half, a wall layer of 

 Four cells surrounds two central cells — primary spermatogenous 

 cells (figs. 22, 23). By rapid growth the antheridium becomes 

 spherical and appears transparent (fig. 26). Its wall cells, however, 

 contain chloroplasts which persist until the sperm mother cells are 

 distinguishable. The wall cells of the upper half grow noticeably 

 larger than those of the lower half. 



No definite cytological study of spermatogenesis was made, but 

 some few points were noted. No centrosome was evident during 

 any division of the spermatogenous cells. The diagonal division of 

 the sperm mother cells separates them by a membrane which 



