2IO BULLETIN OF THE BUREAU OF FISHEiaES. 



was brought in contact with the intestinal fluids, it is not obvious just what purpose would 

 be served by the attachment of the spore to the intestinal wall. In short, it is believed 

 that the function of the capsules which form such a conspicuous part of the spore has not 

 been demonstrated. 



According to Auerbach (1910) and Erdmann (191 there is, even in the "free" 

 forms, a short stage of intracellular existence, the newly emerged sporozoite entering 

 an epithelial cell and multiplying by binary fission. In these species, however, the period 

 of cell parasitism is comparatively brief, and the greater part of their existence is spent 

 in the cavity of the infected organ, either attached to the epithelium or floating freely 

 in the bile or urine. According to Auerbach, the intracellular phase is followed by the 

 fusion of two planonts, the nuclei remaining separate, thus forming a binucleate tropho- 

 zoite, which he believes develops into the spore-forming plasmodiura. The sexual 

 phenomena are, however, so complicated and the accounts of different writers so funda- 

 mentally diverse that it is not thought best to go into the subject at this time. 



THE SPORE. 



Since the spore is practically the only organ in the Myxosporidia having a well- 

 defined structure the details of which are nearly constant for each species, it has always 

 been the principal character used in distinguishing the different species. For this reason 

 it is of the greatest importance to have a clear understanding of the fundamental 

 structure of the spore. Unfortunately most writers have based their conception of the 

 myxosporidian spore primarily on that of Myxoholus. It has already been pointed out 

 that there are good reasons for believing that the Myxobolidae represent the most highly 

 specialized group of the Myxosporidia, and this specialization is as evident in the spore 

 as in the plasmodium. A truer conception of the myxosporidian spore can be obtained 

 from the study of those of less specialized genera, such as Leptotheca or Ceratomyxa. 

 Text figure 2 shows diagrammatically the structure of the spore based primarily on 

 Leptotheca. Surrounding the spore is a thin, tough, transparent membrane, the sporo- 

 cyst (sp'c), which is probably of a chitenoid nature. The sporocyst is composed of two 

 valves, each valve being developed from a single parietal cell. The more or less degener- 

 ate nucleus of the parietal cell {par. n.) can often be distinguished in the mature spore. 

 The valves of the sporocyst are united along the sutural line (5. /.), which usually forms 

 a more or less distinct ridge around the spore. Within the sporocyst are the capsules 

 and the sporoplasm or sporozoite. 



The capsules ° {cap.) are typically two in number, but in some cases there may be 

 only one, as in a few species of Myxoholus, or four in Chloromyxum. Each capsule is 

 formed within a capsulogenous cell {cap. c), which can usually be more or less clearly 

 distinguished even in the ripe spore. The capsules are usually pyriform, sometimes 

 approximately spherical in shape, and drawn out at one side into a short, narrow duct 

 opening to the exterior through a minute pore which is always situated along the sutural 

 line. Surrounding the capsule is a tough, refractive envelope, probably chitenous. 

 Coiled up within the capsule is a delicate filament {fil.), usually of comparatively great 

 length, which is probably of the same material as the capsule, with which it is continuous 



« The capsules have been termed "polar capsules'* by most writers, but I agree with Gurley (1894) that it is better to refer 

 to them simply as capsules, since they are often not in the position indicated by the term polar capsule. 



