OBSEEVATIONS ON THE GREGARINES OF HOLOTHURIANS. 305 



history of the Gregarinida/^ It seems most probable that the 

 animals come originally from the intestine, penetrating from 

 thence into the blood vascular system, and that they get into 

 the intestine by the animal swallowing spores with its food. 



One cannot but be struck, in considering these forms, by 

 the great resemblance of the adult to an ovum, and of the 

 sporozoite to a spermatozoon. Both these resemblances are 

 doubtless due to the action of similar conditions. The adult 

 Gregarine is a resting cell fed by the surrounding tissues and 

 only biding its time to undergo developmental changes, which 

 it commences, as Wolters (9) has shown, by throwing ofiF 

 half the nucleus as a polar body. On the other hand, the 

 function of the sporozoite is to reach and burrow into a cell, 

 for which purposes an elongate shape and locomotory organs 

 are necessary. It is probable, as Schneider (7, p. 94.) has 

 said, that '' the spores must be introduced into the digestive 

 tract, and that the sporozoites, set at liberty by the digestive 

 juice, have the energy necessary to perforate the mucosa.'^ 



List of Works cited in the Text. 



1. KoLLiKEK, A.— " Eigenthiimliche an den Gefassen der Holothuria 



tubulosa ansitzende Korper," • Zeitschr. f. wiss. Zool.,' ix, 1857-8, 

 p. 138. 



2. Schneider, Ant, — "Ueber einige Parasiten der Holothuria tubu- 



losa," ' Arch, f, Anat. u. Phys.,' 1858, pp. 325—329, pi. xii, 



3. Saes, M. — 'Oversigt af Norges Echinodermer,' Christiania, 1861. 



4. CuENOT, L.— " Protozoaires commensaux et parasites des Echinodermes," 



' Rev. Biol, du Nord de la Frauce,' Lille, 1891, p. 298, 



5. MiNGAZziNi, P. — " Le Gregarine delle Oloturie," ' Atti [rendiconti] della 



r. Accademia dei Lyncei,' ser. 4, vol. vii, fasc. 9 (15th Nov., 1891) 

 pp. 313—319. 



6. BtJTSCHLi, 0. — " Protozoa," ' Bronu's Klassen und Ordnungen des 



Thierreiches,' Bd. i, Abth. 1 : " Sarkodina und Sporozoa." 



7. Schneider, Aime. — "Gregariues nouvelles ou peu coniiues," 'Tabl. 



Zool.,' vol. i, Nos. 3, 4: "Syncystis rairabilis," pp. 90—94, 

 pis. xxiii and xi, figs. 1 — 3. 



