222 Barker. — The Morphology and Developinent of 
less dense and more vacuolated protoplasm, and with which 
eventually become associated the nucleus or nuclei which 
produce the nuclei of the spores. The occurrence of nuclear 
divisions during the period of protoplasmic differentiation 
is also typical of both groups. The results of Wager (25 
and 26), Trow (22), Berlese (1), and Miyake (28) on various 
other Oomycetes also agree in most details ; but the zonation 
stage of the nuclei is not so marked, nor is the protoplasmic 
aggregation so pronounced in the early stages. As Stevens 
remarks in connexion with Albugo Candida (21), it is the 
absence of this preliminary aggregation which precludes the 
early marshalling of the nuclei into the form of a hollow sphere. 
There are then many points in common between the methods 
of formation of oospheres in the Oomycetes and of ascospores 
in the Ascomycetes, and further investigation may reveal even 
closer resemblances in the behaviour of the kinoplasmic threads 
during the final mitosis during oogenesis in the former. The 
hypothesis that the oogonium has been evolved from a game- 
tangium, which has been considered by Stevens (21), makes 
those somewhat allied methods of spore-formation of great 
interest in conjunction with the hypothesis of the homology 
of the ascus with the zoosporangium. If it be assumed that 
antheridia and oogonia are homologous with gametangia, it is 
no great step further to admit the evolution of asci from 
zoosporangia, seeing that among the lower Algae gametangia 
and zoosporangia are in many cases identical. The view of 
Harper may therefore not be of such importance as at first 
appeared, especially when it is considered that the structures 
which show similarity in method of spore-formation also 
produce spores of a similar physiological character, the 
presence and survival of the periplasm being thus explained. 
The lack of forms intermediate in character between Oomy- 
cetes of the type of Peronospora omnivor a and Ascomycetes of 
the type of Monascus is a point of some importance because 
of the width of the gap separating these forms. The lower 
Ascomycetes, apart from the Gymnoascaceae, are distinguished 
by a complete loss of sexuality or by its isogamous character, 
