194 Haemogregarina anarrhicliadis 
centrally situated, occupies the whole width of the parasite so that it 
often bulges laterally, and readily overstains with Giemsa or Leishman, 
so that it is impossible, without extraction, to make out the chromatin 
elements distinctly. Moreover, Haemogregarina platessae frequently 
exhibits at one pole a clear vacuole, which is quite absent from the 
catfish haemogregarine. 
The existence of the phases above described, the occurrence of the 
deeply staining polar mass, and the features of the nucleus in the latter 
distinguish it from all previously described piscine haemogregarines 
with the exception of Haemogregarina rovignensis, a parasite found by 
Minchin and Woodcock (1910) in three specimens of a gurnard, Trigla 
lineata, caught at Rovigno on the Adriatic. In both there occur the 
same three phases of development, and the small oval forms are 
closely alike in each case. But in the case of the long thin forms in 
the gurnard haemogregarine their pointed extremities are frequently 
folded back on the main body of the parasite, whereas this appearance 
has never been found in the catfish parasite. It is not improbable 
however that this form does exist, but is obscured in my films from the 
method of preparation employed, for in working with a snake haemo¬ 
gregarine I have been struck with the paucity of forms showing the 
recurved limb in air-dried films as compared with the relative frequency 
of such forms in wet-fixed preparations. Again, in Haemogregarina 
rovignensis the deeply staining polar mass is not so constant as it is in 
the catfish haemogregarine. In the case of the former, too, there is a 
marked difference between the long thin form with a compact nucleus 
and the long thick bean-shaped form w’ith a relatively larger nucleus 
and transitional phases are absent. On the other hand, a striking 
feature in films of the catfish haemogregarine has been the rarity 
of long thin forms and the frequency of stages intermediate between 
these thin forms and the thick reniform type. Also the nucleus of the 
thick forms does not appear to be relatively larger than that of the thin 
type. Such distinctions, of course, may be appai'ent rather than real, 
for in the case of the gurnard parasite the description is taken from 
wet-fixed films, whereas the picture presented by the catfish 
haemogregarine is merely that shown in films fixed after being dried 
in air. 
Lastly, there confronts one the interpretation of the significance 
of the various phases of the parasite found in the circulating blood. At 
the outset one may state that the different forms represent phases in 
the development of one and the same haemogregarine, for there is no 
reason for assuming that they represent different infections, i.e. 
