THE MYXOSPORIDlA, OR PSOROSPERMS OF FISHES. 121 



Plane, transverse:^ Vertical and (usually) post-capsular in position, 

 dividing- (roughly) the spore into a caj)sular (anterior) and a sporo- 

 plasmic (posterior) portion. 



Plane, vertical : Longitudinal and intercapsular, passin^j between the 

 cajjsules and through the ends of the spore and the median cornua of 

 the sporoplasni, and dividing the spore into a right and a left half. 



Posterior: See Anterior. 



Protocysts : The two smaller segments of the MijxohoJus sporoblast, 

 which ultimately form the capsules. 



Protosporoplasm: The larger segment of the Myxobolm sporoblast, 

 which ultimately forms the sporoplasm. 



Ribbon: The shell processes described by Balbiani in Myxoholus ellip- 

 soides (see pp. 223). 



Eibbonettes: The terminal subdivision of the ribbons, termed 

 "filaments" and confounded with the capsular filaments by some 

 writers (see pp. 87, 88, 203). 



Ridge : The ridge or " welt " which extends around the circumference, 

 and marks the line of junction of each valve. 



Ridge index: The ratio of the width of the ridge to the total width 

 of the surface on which the ridge is situated. 



Seat: This term invariably denotes tbe organ or part of the body in 

 which the myxosporidian is located (see also Host). 



Sporoblast (and pansporoblast): This term was first used (in the 

 Myxosporidia) by Biitschli^ for the transparent spherical globule formed 

 by the condensation around one of the nuclei, of a portion of the sur- 

 rounding myxoplasm. The spherical globule so formed subsequently 

 segments into two hemispheres (see p. 81), each of which gives rise to a 

 spore. Now, Balbiani, ^ and Thelohan,* and Henueguy and Thelohan, ^ 

 apply the term sporoblast to the two hemispheres. Further, Pfeifter" 

 uses the term sporoblast as a synonym for the whole sporing myxospori- 

 dium. This latter use of the word should, I think, be unhesitatingly 

 rejected as having no warrant in analogy. By the advice of Dr. C. W. 

 Stiles (who has specially studied the equivalence of this and several 

 other terms'), I have followed the lead of Balbiani and Thelohan in 

 restricting the term sporoblast to the segments (the two hemispheres 

 above mentioned) formed by the division of the primitive sphere.' For the 

 latter (the sporoblast of Biltschli) the term pansporoblast is here used. 



1 Equatorial plane of Lutz, 1889, Centralbl. f. Bakt. ii. Parasitenkde, v, p. 86. 



^Bronu's Thiei-Reicli, 188SJ, i, p. 596. He says : "Since the spores originate from 

 the plasma globules, we may conveniently term tliem Hporohluats." Conqjare also an 

 exceedingly obscure sentence in Biitsclili's next paragraph. 



^ Journ. de Microgr., Paris. 1883, vii, p. 275. 



•• Compt. Rend. Acad. Sci. Paris, 1890, cxr, p. 693. 



6 Annal. de Microgr., Paris, 1892, iv, p. 634. 



"Die Protozoen als Krankheitserreger, 1890, 1 ed., pp. 32, 34, et al. 



•'Notes on Parasites; .Journ. Compar. Med. & Veter. Archives, New York, 1892, xiil, 

 pp. 321-324. 



