114 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES. 



a satisfactoiy clussiliciitiDii ol' tlu! order it will be necessary to utilize 

 additional cliaiacteis, in particnlar those connected with spore t<>pog- 

 raphy and spore symmetry. This brings us to a ctmsideration of the 



SY.MMKTKY OK THK M YXoSI'uKlUIAX SPORE. 



Considering" the importance of tlie ])resence or absejice of symmetry 

 throuiihout the animal kingdom, it is strange tliat no attention lias 

 heretofore been paid to this leature olthe myxos])oriilian spore. These 

 bodies exhibit four varieties of symmetry, viz: 



1. Absence or obscurity ofsymmetri/. — This is found in the Grypfocystes. 

 Anteroposterior symmetry is certainly absent; bilateral and supero- 

 iuferior symmetry (or asymmetry) obscure. 



2. Bilateral symmetry (symmetry around the vertical plane). Present 

 in all genera of Fhanocystes except Ceratoiny.ra,^ which is asymmetric 

 as regards the position of the sporoplasm. 



3. Snpero-inferior syinmetry (dorso-ventral symmetry: symmetry 

 around the longitudinal plane). — This is the rule in the Phwiiocystes, 

 but as no attention has been directed to the detection of asymmetry, 

 it may be that it is present in a few species. It certainly forms a 

 striking feature of Myxobohis macrnriis, in Avhich the difterentiation of a 

 dorso-ventral axis is perfectly plain. Further, the supero-median cornu 

 extends farther forward than the inferior median cornu in several (all 

 examined by me) Myxoholus species, furnishing another indication of 

 this diiferentiation and a clue to the homology of the superior and 

 inferior surfaces in ditierent spores (see pp. 122, 235). 



4. Antero posterior symmetry (symmetry around the transverse plane). 

 This type appears to be characteristic of, and confined to, the genus 

 Cystodiscus, in which antero-i)osterior symmetry is equally present, 

 whether we regard the extremities of the spores as (anterior and pos- 

 terior) ends or as (right and left) wings. 



The importance, for classification, of a study of spore symmetry is 

 soon seen. Employing the knowledge thus obtained for the purpose of 

 orienting the spore, we find that the characters of greatest taxonomic 

 value are: 



1. Spore topography. — Thus in Myxidium lieberJcUhnii the presence of 

 bilateral and the absence of anteroposterior symmetry show that the 

 two pointed extremities of this spore, heretofore, like all other pointed 

 extremities, loosely termed " ends," do not correspond to anterior and 

 posterior, but to right and left. On the other hand the "ends "in 

 Cystodiscus appear to represent ends scjis. strict., i. e., to correspond 

 to anterior and posterior. 



>Witli the further exception of two Mi/xobohta species (M. unicapsulatus with only 1 

 capsule, and M. inequaJis with 2 unecjual capsules), which, ou account of reduction 

 of characters, have suffered a correspond in <; loss of the perfect symmetry character- 

 istic of the genus. To make the exception absolutely complete, M. strongylurua may 

 be added (see p. 249;. 



