The terms intracapillary, interlamellar, cutaneous and visceral are proposed as names for four working forms or categories of Henneguya spp. found in channel catfish. Guidelines for their proper identification are suggested and the severity and incidence of each form are documented. Disease workers in diagnostic laboratories often find it convenient to separate Henneguya spp. infections into forms based on the nature of induced lesions. These forms include the interlamellar form, intracapillary form, which is referred to by many workers as the intralamellar form (Meyer, 1972, personal communication), visceral form, and cutaneous form. These working forms or categories are classified according to their location within the host tissue. The usefulness of such non-taxonomic divisions will be readily apparent when the pathogenicity and frequency of occurence of each form are considered. Before these working categories can be effectively used, some agreement as to their proper identification needs to be reached. With this goal in mind, I submit the following observations which, hopefully, will help to clarify this sometimes confusing problem. The cutaneous form includes all cysts which affect or involve the skin, such as those found in the adipose fin, dermis, and dermal "tumor-like" external growths (Fig. 9). The visceral form includes those cysts associated with the various internal organs, such as the kidney and liver. Economically, these forms are of little importance as they are observed rarely (Table I) and then cause only light mortalities. A low percentage of the infected fish may be so disfigured they cannot be sold. The intracapillary form includes those cysts which are confined within the capillary walls of a single lamellae as pictured in Figures 4 and 5. Several characteristics of these cysts and of the surrounding tissues are consistent enough to be useful in diagnostic work. In well-sectioned H&E stained material, red blood cells are almost always visible surrounding the entire cyst (Figs. 4, 5). Also in serial sections a capillary surrounding the cyst and opening into an arteriole should be visible (Fig. 5). In most sections, the outer epithelial membrane surrounding the lamella remains identifiable around the entire cyst (Figs. 4, 5). In large mature cysts these features are sometimes not as distinct but are generally still visible in well-stained sections. Another prominent characteristic is that a small immature cyst generally develops in the capillary from the tip of the lamella (Fig. 4) towards the base (Fig. 5).
