Thom — Fertilization in Aspidium and Adiantum. 295 



diameter. If it were a solid mass of chromatin, it would 

 require much more such material than we find in the 

 nucleus of the spermatid, which is scarcely six microns in 

 diameter. Schottliinder in his observations on the spermato- 

 zoid of Aneura pinguis finds a similar ground substance in 

 the center of the nuclear portion surrounded by a chromatin 

 layer. Zacharias ('87) in investigating the spermatozoids of 

 Chara has shown by micro-chemical means that the ciliate 

 anterior end and vehicle behind are cytoplasmic. By diges- 

 tion experiments he succeeded in dissolving the chromatin, 

 leaving the anterior end and the cj- toplasmic posterior end con- 

 nected by the cytoplasmic envelope and a delicate fiber (zarte 

 Faden) in the center whose nature remained undetermined. 

 By digesting the nuclear portion Strasburger demonstrated 

 the cytoplasmic envelope of the nucleus but does not mention 

 a central filament. Belajeff by a similar experiment found 

 the two ends connected by a slender thread, which may have 

 been either this central filament or the cytoplasmic layer on 

 the outside. These tests show that the cytoplasmic forward 

 end and the connecting fiber react in the same way as the 

 kinoplasm of the spindle fibers, which would fix them as 

 kinoplasmic structures. The same central filament is de- 

 scribed by Franze ('93) as " Achsenfaden." On the basis 

 of my own observations it seems to be nuclear in origin and 

 probably represents some transformation of the large amount 

 of nucleolar material present in the earlier stages. 



To recapitulate the structure of the spermatozoid of the 

 fern as now understood : — The entire body forms a left- 

 handed screw or spiral about forty microns in length and pos- 

 sibly three microns in greatest diameter. The anterior 

 cytoplasmic portion forms about two spiral turns inclosing a 

 body or thread derived from the " Nebenkern " or " blepha- 

 roplast " which bears the cilia. The central portion of the 

 two much larger and longer coils consists of the nucleus and 

 its cytoplasmic envelope. The diameter of the nucleus in- 

 creases from a pointed end in front to a blunt end behind. 

 The posterior portion is a cytoplasmic vesicle attached to the 

 inside of the last coil of the nucleus. The cilia, according to 

 Belajeff, exceed forty in number. They are, for the most 



