.^84 ^r>'. T. Bcntliain nn some 



quite resistant to tlic influence of tlie lia-niolysiu, and fall 

 distinctly into two categories. Sliort forms are present of 

 the usual llaMnogregariuc ty})e, naniely, bean-sliajied and 

 rounded at both ends, with a more or less centrally placed 

 nucleus of the difl^use type. They measure roughly 10 /x in 

 length by 3 /I in breadth, and inter se do not vary very 

 much in size. These forms were taken to be the micro- 

 gametocytes, or those destined to give rise to the male forms 

 of the parasite. They were further characterized by being 

 free from all metachromatinic or volutin granules, and in this 

 character they differ from the intra- and extra-cellular para- 

 sites found in the peripheral blood of Cotius (see PI. XVI. 

 fig. 1, 3h). The female elements or macrognmetocytes were 

 elongate vermicular forms — as a rule, about 15 /ju by 2 to 3 ft 

 in measurement, and having a conijiact vesicular nucleus 

 situated about the middle of the cell-bod3\ This nucleus 

 usually contained a large distinct karyosome situate within 

 the organ. No external chromatin grains were to be seen, 

 and, as in the microgametocytes, the cytoplasm was free from 

 volutin. The rest of the life-history in the leech could not 

 be made out with certainty, but there were present in the gut 

 a fair number of large rounded bodies having a more or less 

 compact nucleus. In some cases what appeared to be an 

 extrusion of karyosomes could be made out. These large 

 forms were taken to be macrogametocytes which had passed 

 into the macrogamete stage. No stages of the formation o£ 

 microgametes could be seen (see PI. XVI. fig. 1, 2 a & 2b). 

 It was at first thought that the elongate vermicular forms 

 might jiossibly be Ciithidial stages of Trypanosomes present 

 in the leech-gut, and to this end smears were stained with 

 iron hematoxylin. With this process the structure of the 

 nucleus was seen to approximate more closely to the usual 

 Haemogregarine type, rather than to the appearance of the 

 same structure in a Trypanosome. From these observations 

 it is therefore fairly evident that schizogony takes place, not 

 in the blood of Cotius, but in the spleen, the gamogonous 

 cycle taking ])lace in the gut of the invertebrate host. It is 

 also evident that the spores of the genus Ilcemogregarina are 

 very resistant of death and dissolution in the invertebrate 

 host, since they seem to persist for a very long time in the 

 dorsal blood-vessel of the leech. This is substantiated by 

 the following facts. A cat-fish {Atiarrhichas lupus) was 

 caught on one of our trawling-trips near Holy Island on 

 June 25th, 1913. Several specimens of the leech Ichthyo- 

 hdella anarrhichcB were taken from the gills and placed in 

 a glass vessel in the aquarium. These leeches were kept 



