662 Blackman.—The Primitive Algae 
Chi. Ehrenbergii (Fig. 13) the walls are thrown off at the 
moment of union of the gametes, so that the two shells are 
found close to the resulting zygote; and finally, with Chi. 
multifiiis fusion advances so far before the walls are actually 
discarded that the walls are left fused together at one part 
to form a single shell. 
We have thus a series of forms, of which the last-mentioned 
is presumably the most primitive ; from this we proceed up to 
gametes devoid of walls from their first formation. 
The lower end of this remarkable series would be com¬ 
pleted if we had a form in which the gametes conjugated by 
uniting inside their walls without throwing them off at all. 
Goroschankin (’ 90 ), in a separate and very complete paper, has 
shown that this is exactly what occurs in Chi. Braunii {—Chi. 
pulvisculus , Stein). In this species (Fig. 13), however, the 
walled gametes are of different sizes (heterogamous), and in 
their later stages non-motile by loss of their cilia, so that this 
form cannot take its place directly at the lower ends of an 
isogamous series. The smaller (male) gamete is about half 
the size of the female one; when they have swarmed close 
together the cilia are lost, and processes of the wall are put 
out at adjacent spots. These meet and fuse and form a canal, 
through which the contents of the smaller gamete pass over 
into the larger one. A wall is then formed in the canal, and 
the protoplasts of the two gametes fuse completely and form 
a zygote inside the wall of the female gamete. Occasionally 
several male gametes attach themselves to one female, but 
the contents of one only of them passes into the female. The 
similarity of this process with that occurring with the non- 
motile cells of Spirogyra and other conjugates is most 
remarkable, and it has been suggested that this is of real 
phylogenetic significance. At present we need only dwell on 
the variety of process found in this single genus from one 
extreme of the union of heterogamous walled aplanogametes 
to the other of the union of isogamous naked planogametes. 
In addition to these forms Klebs (’ 96 ) has described a new 
species, Chi. media (Fig. 13), which shows a slight variation 
