Genera: _Saprolegnia_, whose swarmspores disperse immediately after having left the sporangium. _S. ferax_ is the cause of a disease in fish (“Salmon disease”) and in the crayfish.--_Achlya_, whose swarmspores accumulate in a hollow ball before the mouth of the sporangium.--_Leptomitus_ has strongly indented hyphæ, causing a “linked” appearance. _L. lacteus_ is frequent in the waste matter from sugar factories.--_Monoblepharis_ deviates from the others by the greater development of its fertilising process; the oosphere, situated in an open oogonium, becoming fertilised by self-motile spermatozoids, which are provided with a cilium at the posterior end. Class 2. =Mesomycetes.= The Mesomycetes are intermediate forms between the Phycomycetes and the Higher Fungi. In the vegetative organs, and in the multicellular hyphæ, they resemble the Higher Fungi; the methods of reproduction, however, show the characters of the Phycomycetes, namely sporangia and conidiophores of varying size and with varying number of spores; definite and typically formed asci and basidia are not present. Sexual reproduction is wanting. The HEMIASCI are transitional between the Phycomycetes and the Ascomycetes, the HEMIBASIDII (Brand-Fungi) form the transition to the Basidiomycetes. Sub-Class 1. =Hemiasci.= The Hemiasci are Fungi with _sporangia_ which, _although resembling asci_, yet have _not_, however, _a definite form and a definite number of spores_. Besides endospores, conidia, chlamydospores and oidia are found. Order 1. =Ascoideaceæ.= _Ascoidea rubescens_ forms irregular, reddish-brown masses in the sap issuing from felled Beeches. It has _free sporangia_, which resemble asci in their structure, in the development and ejection, and in the definite shape and size of the spores. The formation of the sporangia takes place when the nutriment is nearly exhausted, and resembles that of the conidia, since they are developed from the end of a hypha which enlarges, and the swelling becomes separated by a transverse wall. Within the sporangia numerous spores of a cap-like form are developed, which are set free through an opening at the apex. Sporangia are formed successively at the apex of the same hypha, the second commencing to develope as the first is dehiscing. Conidia and sporangia are not formed simultaneously; the former may be considered as closed sporangia. Order 2. =Protomycetaceæ.= _Protomyces pachydermus_ causes hard swellings on the stems and leaf-stalks of the Cichorieæ (_Taraxacum_, etc.). These swellings consist of _chlamydospores_ (resting-spores), which germinate and become free, ascus-like sporangia, with numerous small spores. In nutritive solutions the chlamydospores form conidia with yeast-like buddings. _P. macrosporus_ on _Ægopodium_, and other Umbelliferæ.