55i 
Dietyota and Taonia. 
to six times the diameter of the head. It has to be borne 
in mind that in the spermatozoids of Himanthalia and 
Cystoseira , which as already stated are very similar to those 
of Dietyota in the shape of the head, there is great disparity 
in length between the two cilia, one being very short while 
the other is correspondingly long. The possibility suggested 
itself that this might be the case here, one being so much 
reduced as to be almost invisible. In spite, however, of the 
greatest care taken in observing, no trace of a second cilium 
was seen. The probability that there is only one flagellum 
to each antherozoid is strengthened by the following facts : — 
1. The flagellum in the great majority of cases proceeds in 
a radial direction from the head (see Fig. 2) instead of being 
directed tangentially to it as in the Fucaceae. Antherozoids 
of Himanthalia were fixed and dried for comparison. In 
spite of the rough treatment the biciliate character and the 
tangential attachment were clearly shown. 
2. In the glycerine-preparations the flagellum is strikingly 
spiral (Fig. 3); this never occurs in the Fucaceae. 
3. As already stated, the character of the movement was 
suggestive of the presence of a single flagellum. 
When the glycerine-preparations are examined it is seen 
that instead of consisting of hyaline protoplasm, as described 
by Thuret \ the head of each antherozoid shows clear and 
unmistakable differentiation of structure. The greater part 
of it appears clear and transparent, while one side is occupied 
by a thin layer of denser protoplasm staining deeply with 
Hoffmann’s blue. When viewed in profile this seems cres- 
centic in form, with the inner border often wavy but always 
sharply defined. The comparison of a number of antherozoids 
lying in different positions shows that this denser protoplasm 
forms a lining of approximately circular form but with an 
irregular, wavy, often indented border. It may be compared 
to a watch-glass with an irregular, indented rim (Fig. 3). The 
small spherical body already mentioned is most often close 
Loc. cit. 
