JOURNAL OF MICROSCOPICAL SCIENCE. 



DESCRIPTION OF PLATE XX, 



Illustrating Mr. Ray Lankester's Notes on the Structure of 

 Gregarinse, and on the Development of G. Sipunculi. 



Fig. 1. — Gregarina {Monoc^siis) Ascidice observed at Naples; tf, </, spaces 

 in the medullary substance devoid of granules ; 7ii, fiiarillated 

 contractile expansion of the cortical subtauce. Length, g^th 

 of an iuch. 



,, 2. — Gregarina {Monocystis) Nereidis, showing, m, the mobile fibrillated 

 enlargement of the cortical substance, 



„ 3. — Gregari7ia {Motioci/stis^ Zygocystis, Stein) Sipunculi; a gigantic 

 specimen magnified 25 diameters, found actively swimming in 

 the perivisceral fluid of Sipuneulus nudus at Naples. The s])e- 

 cimen is seen to consist of two individuals united either by 

 apposition or by division of one original individual. Fig. 3 a. 

 A similar specimen of the natural size. Fig. 3 b. Spherical 

 (encysted) specimens of the natural size. Fig. 3 c. Sector of a 

 spherical specimen which is encysted in a sheath of the ciliated 

 peritoneal membrane of the Sipuneulus. The characteristic 

 isolated ciliated tufts of this membrane are seen on the surface 

 of the cyst, to which they give a rotatory movement, 



,. 4. — Optical section as seen at the margin of the specimen drawn ui 

 fig. 3 ; a, tuberculate cuticle ; b, deuse, structureless corticrd 

 layer; c, granular medullary substance. 



,, 5. — Surface view of the tuberculate cuticle of the specimen fig. 3. 



„ 6. — a, immature pseudo-navicula of G. Sipunculi, from a cyst in the 

 perivisceral membrane of Sipuneulus nudus ; b, c, d, e, mature 

 pseudo-naviculse, from a 'similar cyst. They are provided wth 

 a motionless filament. Length of the pseudo-navicula about 



•2o\)o*'l' ot" ^1 inch. 

 ,, 7. — Newly hatched, rapidly moving pseudo-filariaj of G. Sipunculi, from 



cysts in the intestinal wall of Sipu7iculus midus. 

 „ 8. — Further advanced, with commencing nucleus. 

 „ 9. — Commencing transverse division, 

 ,, 10, IL — The posterior actively moving "tail" is marked off from the 



immobile, more fully developed " head," forming the pseudo- 



cercaria, 

 „ 12, 13. — The separated anterior and posterior segments. 

 ., 14. Further development of 12 to a true Gregarina form. This specimen 



presents a double nucleus. 

 „ 15. Multiplication of the smallest Gregarinae by longitudinal fission. 

 „ 16, 17. Stages in that process, 



,, 18. A young i)io«ory4'^zs 6'2);m«c?^/?, -jT^Qth of an inch long. 

 „ 19. Pseudo-uaviculse of Gregarina {Monccystis) Scenuridis which 



were observed in prodigious quantities in cysts and liberated 



in the perivisceral cavity of a specimen of Tubifex rivulorum. 



They possess a motionless filament similar to those of some 



psorosperms. 



