2o8 BULLETIN OF THE BUREAU OF FISHERIES. 



accomplished entirely by these short, conical, or branched pseudopodia. The same is 

 usually true of trophozoites which have been on the slide for some time, locomotion 

 in such cases becoming slower and the filiform pseudopodia entirely disappearing. 



REPRODUCTION AND INFECTION OF NEW HOSTS. 



In the case of parasitic protozoa Doflein (1898) has distinguished between multi- 

 plicative and propagative reproduction. The former results in the increase of the para- 

 site within the host ; the latter provides a means by which the parasite may gain entrance 

 to a new host. 



There is still a great deal of uncertainty regarding the methods of multiplicative 

 reproduction in the Myxosporidia, and more knowledge on the subject is badly needed. 

 It is, however, a problem which is peculiarly difficult of solution, especially in the "free" 

 forms. According to Doflein, multiplicative reproduction in these forms is entirely by 

 plasmotomy. In most cases the plasmodium separates into two equal or nearly equal 

 parts. However, in Myxidium lieberkiihni, according to Cohn (1896), multiplicative 

 reproduction is accomplished by a method of exogenous budding. In a former paper 

 (Davis 1 91 6) reasons have been given for believing that the process observed by Cohn 

 is abnormal and has nothing to do with reproduction. In Sinuolinea dimorpha (Davis 

 1 91 6), a method of multiplicative reproduction by endogenous budding has been demon- 

 strated. This method consists simply in the formation of gemmules from the generative 

 cells within the mother trophozoite. These later emerge and give rise to new individ- 

 uals. There is evidence that a similar process occurs in several species of Ceratomyxa 

 and Sinuolinea, and the writer has no doubt that this is a common method of multipli- 

 cation among the "free" forms. Possibly this method may be considered a form of 

 plasmotomy, but if so it is certainly quite different from the process described by 

 Doflein. 



In the tissue parasites multiplicative reproduction by a process of multiple division 

 or schizogony has been described by Doflein, Keysselitz (1908), Nemeczak (191 1), and 

 Hahn (1915). 



Propagative reproduction, so far as known, is always by means of spores, which 

 enables the organism to resist the unfavorable conditions which it may encounter in gain- 

 ing entrance to a new host. The process of sporulation is a very complicated one and 

 can not be gone into here. (See Auerbach (1910), Minchin (1912), and Davis (1916).) 

 The spores are usually formed in pairs, each spore being composed of six cells (eight in 

 Chloromyxum). Two of these cells form the outer protective covering, the sporocyst; 

 two form the capsules; while the remaining two cells form the binucleate sporoplasm. 

 The number of spores formed by a single trophozoite varies from one to a large number, 

 and we often find considerable variations in this respect within the same species, for 

 example, Ceratomyxa multispora and Sinuolinea dimorpha. In the case of the mono- 

 sporous and disporous trophozoites the spores are set free by the death and disintegration 

 of the mother trophozoites. In the polysporous trophozoites the spores may all be formed 

 at the same time, as in the disporous forms, and liberated in the same way. More com- 

 monly, however, the formation of spores continues for some time, the mature spores 

 being successively set free as new ones develop. 



