GREGARINIDA. 25 



and pseudo-naviculas arc then produced. Wo Iiave now to follow tlie development of 

 new generations from these s])ores. 



The development of the pseudo-naviculaj has not been fully made out, except in a 

 few cases. It is probable, however, tliat their granular contents escaj^e, and form 

 ainceboid masses from which the Gregarines are either directly or indirectly developed. 



In tlie intestine of the lobster naked protoplasmic masses have been observed, 

 which, as will be seen, have been proved to belong to the Gregarines. In the perivis- 

 ceral cavity of the earthworm the encysted Gregarines, Gregarina Iwnhricus, are often 

 found in great abundance. There the pseudo-naviculae are set free in innumerable 

 quantities, and their contents have been observed to produce ama»boid bodies from 

 which new generations of parasites originate. 



The Gregarine of the lobster, P. gigantea, according to E. Van Beneden, develops 

 from an amoeboid form, but the course of delevopment differs somewhat from that 

 observed in the case of the Gregarine of the earthworm. Within the intestine of the 

 lobster the minutely granular amceboid form from which the parasite develops was 

 found destitute of both nucleus and membrane, re&emhWng Protamceba primitioa, or 

 P. agilis, Haeckel, but not projecting true pseudopodia. These amceboids become 

 converted into spherical, motionless globules, the "generative cytodes," which finally 

 develop two projecting processes, resembling the stalk of JVoctiluca, from which the 

 Gregarines are directly develojied. One of the prolongations is longer than the other. 

 The longer one separates from the cytode and then moves about independently, like a 

 nematode worm. The shorter arm then develops, appropriating the entire substance 

 of the cytode, and likewise acquires the form of a nematode worm. These the author 

 has designated "pseudo-filarite." After some changes in form they cease to move, a 

 nucleolus and then a nucleus forms about the middle of the body, and finally a new 

 Gregarine is developed directly from them. 



In the development of the Gregarinida we find a complete genealogical, phylo- 

 genetic hi.story of the cell. From the psorosperms are derived plasmic bodies, devoid 

 of nucleus or external envelope, allied to the plastidules of the Monera, already described 

 on jjage 3, naked cytodes, which are the lowest and simplest forms of living mattei-. 

 Then a denser layer of sarcode is formed, corresponding to the ectosarc of rhizojiods, but 

 still there is no nucleus. Soon a nucleus and nucleolus is differentiated from the proto- 

 plasm, and the cytode becomes a perfect cell. This transformation may take place 

 directly, or, as in the case of Psorosperma gigantea^ by the budding of the cytode and 

 the development of nuclei within the separated buds. The cycle is completed by the 

 gi-owth of the young Gregarine, its encystment, and finally the production of the jjsoro- 

 sperms. 



The Gregarinffi are divided into two divisions, Monoeystidea and Dicystidea, accord- 

 ing as the body is composed of one or two sacs. Schneider, who has given the most 

 complete account of these forms, recognizes eighteen genera of GregarinsG, represented 

 by about thirty species. Our American forms have been scarcely touched, Dr. Leidy 

 alone having investigated them. 



RoMYN Hitchcock. 



