114 REPORT OF THE COMMISSIONER OF FISH AND FISHERIES, 
a satisfactory Classification of the order it will be necessary to utilize 
additional characters, in particular those connected with spore topog- 
raphy and spore symmetry. This brings us to a consideration of the 
SYMMETRY OF THE MYXOSPORIDIAN SPORE. 
Considering the importance of the presence or absence of symmetry 
throughout the animal kingdom, it is strange that no attention has 
heretofore been paid to this feature of the inyxosporidian spore. These 
bodies exhibit four varieties of symmetry, viz: 
1. Absence or obscurity of symmetry.—This is found in the Cryptocystes. 
Antero-posterior symmetry is certainly absent; bilateral and supero- 
inferior symmetry (or asymmetry) obscure. 
2. Bilateral symmetry (Symmetry around the vertical plane). Present 
in all genera of Phenocystes except Ceratomyxa,' which is asymmetric 
as regards the position of the sporoplasm. 
3. Supero-inferior symmetry (dorso-ventral symmetry; symmetry 
around the longitudinal plane).—This is the rule in the Phenocystes, 
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 Myxobolus macrurus, in which the differentiation 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) Myxobolus species, furnishing another indication of 
this differentiation and a clue to the homology of the superior and 
inferior surfaces in different 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-posterior 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 Myxidiwm lieberkiihnii the presence of 
bilateral and the absence of antero-posterior 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 sens. strict., i. e., to correspond 
to anterior and posterior. 
!With the further exception of two Myxobolus species (M. unicapsulatus with only 1 
capsule, and M. inequalis with 2 unequal capsules), which, on account of reduction 
of characters, have suffered a corresponding loss of the perfect symmetry character- 
istic of the genus. ‘To make the exception absolutely complete, M. strongylurus may 
be added (see p. 249). 
