Natural History of the Vortlcellae. 471 



EXPLANATION OF THE PLATES. 



Plate XII. 



Figs. 1-6. Representation of the asexual propagation by bifission of Vor- 

 ticeUa marina (sp. n. ?). 



1. Commencement of the division by retraction of the ciliated organ 



and contraction of the whole body, with increase of the trans- 

 verse diameter. 



2. Segmentation and gradual deepening of the constriction which 



divides the body into two similar halves : the nucleus Qi) and 

 contractile vesicle are divided at the same time. 



3. Division completed : one fissional scion is separating from the 



peduncle and forming the posterior circlet of cilia (n). 



4. 5, & 6. Free, swarming fissional scions. 

 Figs.l-W, Fission of CotJmrnia itnberbis. 



7. The animal reti-acted within its envelope. 



8. Constriction into two halves. 



9. One fissional scion separating from the envelope and forming the 



posterior circlet of cilia (m). 

 10 & 11. Fissional scions which have swarmed out of the envelope. 

 Fiff. 12. Single Cothurnia extended out of its envelope : the arrows indi- 

 cate the cun-ent of rotation in the interior ; the cuticula shows 

 a distinct transverse annulation. 



Plate XIII. 



Fiffs. 1-7. Representation of the various stages of "gemmiform conjuga- 

 tion" in Vorticella marina: A;, the bud-like Vorticella ; /, con- 

 tractile vesicle. 



1. The bud-like fissional scion {k) furnished with the posterior circlet 



of cilia has attached itself to a larger Vorticella for the purpose 

 of conjugation. 



2. The conical hinder part of the body of the bud-like Vorticella is 



retracted, and the base thus converted into a sucking-cup. 



3. The vmion is completed by means of this sucking-cup. 



4. The pressure during the amalgamation, which is constantly be- 



coming finner, is so strong that bead-like drops of parenchyma 

 make their appearance round about the point of union. 



5. The bud-like Vorticella has become contracted into a mere 



tubercle. 



6. The contents of the bud-like Vorticella have completely passed 



into the larger Vorticella, so that merely the external sac of in- 

 tegument remains projecting from the latter as an empty lobe. 



7. The cutaneous lobe is thrown off" after some time : the spinous 



appearance usually observable upon it is produced by the col- 

 lapsed, annulated cuticula. 

 Fig. 8. Gemmiform conjugation in Vorticella campanula (see p. 467). 



Plate XIV. 



Fig. 1. Carchesium polypinum : m, mouth; 6, 'contractile vesicle; w, nu- 

 cleus ; k, bud-like scion in the act of attaching itself to a larger 

 Vorticella ; s, nucleiform corpuscles arranged in longitudinal 

 seiies following the course of the muscles. 



Fig. 2. Nucleus of Carchesium polypinum after gemmiform conjugation : 

 e, nuclei. 



