MYXOSPORIDIA 307 



THE SPORE 



As was pointed out briefly in the last section, the spore is still 

 the most important stage of a myxosporidian from taxonomic 

 point of view ; in other words, in order to establish the myxospori- 

 dian nature and subsequent generic and specific identification, one 

 must observe the spore. In this section, the structure of myxo- 

 sporidian spores will be considered. 



The spore of myxosporidia is covered by a shell or spore mem- 

 brane which is composed of two valves which come in contact in 

 the sutural plane and which are usually symmetrical in form and 

 similar in size. \\ hile in some species of Clilorornyxiim, the sutural 

 line which marks the sutural plane, may be very indistinct, it is, 

 as a rule, quite distinct and straight ; in the genera Siniiolinca and 

 Unicapsiila, it may be sinuous. The margin of each valve is more 

 or less thickened, which results in the formation of the sutural 

 ridge. The shell-valve is usually uniform in thickness; in some 

 species of the genus Myxobolus, however, it may differ consider- 

 ably in dift'erent parts of the valve. The surface of the shell may 

 be smooth or may exhibit various markings. ]\Iore or less con- 

 spicuous ridges varying in number and form in different species, 

 may run parallel to the sutural line, may show a network-like 

 structure or may exhibit short tooth-like processes arising from 

 the sutural ridge and radiating toward the center of each valve. 

 When the ridges are fine, they form delicate striations, arranged 

 usually parallel to the sutural Hue. Though these markings are 

 ordinarily seen in znvo, they are very often readily studied in 

 stained preparations. 



The form of the spore varies greatly owing to the difference in 

 the shell-valves together with variously developed appendages : ( i ) 

 lateral appendages as in Ccratoinyxa; (2) anterior processes as in 

 Myxoproteus; (3) posterior processes as in JVardm (fringe-like), 

 Mitraspora (filiform), Hofcrellus (spinous), Henneguya and 

 Agarella (tail-like), etc. 



Inside of the spore membrane are present one, two or four polar 

 capsules and usually one sporoplasm. Gurley (1894) and Davis 

 (1917) used the term "capsules" instead of the polar capsules. It 

 is, however, better to use the old term, in view of the fact that 

 these polar capsules are situated at or near the more or less at- 

 tenuated anterior end in the great majority of genera and species 



