THE OENUS SPIROCHETA AND ALLIES 217 



sexual generation, is a free-swimming medusa or jelly fish, the other, 

 an attached and often branched asexual hydroid. The greatest con- 

 fusion grew out of the fact that each of these generations received a 

 distinct name and were supposed to be different forms of animal life. 

 The medusa phialidium, for example, was regarded as independent 

 at first, but later was shown to be only the sexual generation of the 

 hydroid clytia ; the genus eucope also was proved to be only the medusa 

 of the hydroid obelia. With the increased knowledge of the life history 

 of these forms of coelenterates the confusion was gradually cleared, 

 and the group is now well understood. It was found that some 

 medusse have no hydroid generation, and that some hydroids have no 

 medusae, and such forms were classified in appropriate subdivisions. 

 So it will be, probably, with the hemosporidia; some others, like the 

 Leishman-Donovan bodies, may be found to have a flagellated stage; 

 babesia, for example, is said to have such a stage by some observers 

 (Kinoshita), while certain others have labored hard to make out a 

 flagellum in one form of plasmodium. Others, like Plasmodium 

 malarias and P. vivax, are certainly obligatory cytozoic forms. 



Some forms of parasitic flagellates are of such doubtful structure 

 that the taxonomic position must be left in abeyance. The much- 

 discussed spirochetes, for example, when all is said, cannot be dis- 

 tinguished from certain spiral forms usually classed with the bacteria, 

 and transitional forms bridge the gap between the protozoon Spiro- 

 cheta balbianii and Spirocheta plicatilis, and the bacterial form 

 Spirillum gigantea and Spirillwn recurrentis. It is possible that some 

 morphological or developmental feature may be found ultimately 

 which will permit of a definite limitation of the two types, but it is 

 equally possible that future research will demonstrate the close affinity 

 of the supposedly different types, and to my mind the present con- 

 ditions of facts indicate the latter and not the former alternative, and 

 justify the non-committal term spirillochetidse as a family name for 

 the contested forms. Certainly, the spirochetes are so close to the 

 spirillse that hard and fast lines cannot now be drawn, and, like the 

 phytoflagellates and the lowest plants, the questionable forms indicate 

 once more the high mutability of the group. 



THE GENUS SPIROCHETA AND ALLIES. 



C. G. Ehrenberg, in his masterly treatise on the Infmionsthier- 

 schcn, published in 1838, described spirocheta and spirillum as 

 follows : 



28th Genus. Spirocheta : Animal e familia Vibrioniorum, divisione 

 spontanea imperfecta in catenam tortuosam S. cochleam filiformen 

 flexibilem elongatum. 



