2o6 BULLETIN OF THE BUREAU OF FISHERIES. 



characteristic shape of the trophozoite is undoubtedly due to the presence of this firm 

 outer layer, which also serves for protection and furnishes the means of locomotion, 

 the pseudopodia being always chiefly and in many cases exclusively of ectoplasm. 



The endoplasm has a more fluid structure than the ectoplasm and can usually be 

 easily distinguished by its distinctly granular appearance. It contains numerous nuclei, 

 many of them inclosed in distinct cells, and in addition various metaplasmic products, 

 such as fat globules, pigment granules, and crystals of various kinds. These may in 

 some species be distributed uniformly throughout the endoplasm; in others their dis- 

 tribution is markedly irregular. In pyrLform trophozoites they are usually much 

 more abundant near the anterior end than elsewhere. In at least one instance {Sinuo- 

 linea dimorpha) the endoplasm also contains food particles in various stages of disinte- 

 gration. It is often more or less distinctly vacuolated, the distinctness of the vacuoles 

 varying greatly even in the same individual. The endoplasm, in several species of 

 Ceratomyxa and Leptotheca, has a very remarkable structure. In addition to granules 

 and fat globules it contains large numbers of spherules, which are often so abundant 

 as to entirely fill the endoplasm, with the exception of a short distance at the anterior 

 end. These spherules vary greatly in size in different species and may be homogeneous 

 throughout or inclose crystals or pigment granules. The consistency of the spherules 

 may vary greatly in individuals of the same species. Sometimes they are so firm and 

 dense as to retain their shape perfectly on drying; in other individuals they are much 

 more fluid and easily distorted and in extreme cases may apparently break down into 

 a watery substance. It is still a question whether adult trophozoites of the same species 

 may occur in two extreme conditions — one with well-defined, dense spherules, the other 

 with no trace whatever of spherules — and in all intermediate conditions. This is doubt- 

 less true in the case of very small trophozoites, the spherules only appearing as they 

 grow larger, but there is also evidence that full-grown trophozoites may sometimes fail 

 to develop spherules. In a few cases, notably in Ceratomyxa aitenuata, rod-shaped 

 bodies strikingly like bacteria were present in the endoplasm. 



The sole method of locomotion is by means of pseudopodia, which vary greatly in 

 shape and structure in different species. Sometimes they are long and filiform, in other 

 cases short and conical, in still others branched or even arborescent, or, finally, they may 

 be broad and coarsely lobate. In pyriform trophozoites, in addition to the numerous 

 filiform pseudopodia, there is usually a rapid wavelike movement of the ectoplasm at 

 the anterior end, very characteristic and very difficult to describe. 



There is still considerable uncertainty in regard to the actual mode of progression 

 among the Myxosporidia. In the case of those having lobose pseudopodia the problem 

 is the same as in Araeba, and it is unnecessary to consider it further here. But in 

 most species of Ceratomyxa and Leptotheca the trophozoites are pyriform and capable 

 of comparatively rapid progressive movements in one direction only. Consequently a 

 large, rounded, anterior end can be distinguished, while the posterior end usually termi- 

 nates in a long, slender, tapering process, termed, by Doflein (1898) the " Stemmpseudo- 

 podien. " At the anterior end are formed numerous, long, filiform pseudopodia. 

 According to Doflein, locomotion in such cases is chiefly due to the " Stemmpseudo- 

 podien," which by elongation pushes the body forward. However, after a careful 

 study of the movements of such trophozoites, the writer is convinced that locomotion 

 is due entirely to the pseudopodia at the anterior end. Many times trophozoites have 



