On the Development and Minute Anatomy of the Infusoria. 471 



185. Epeira scalaris. 



Epeira scalaris, Walck. Hist. Xat. des Insect. Apt. t. ii. p. 46 ; 



Hahn, Die Arachn. B. ii. p. 27. tab. 47. fig. 114; Blackw. 



Linn. Trans, vol. xix. p. 127. 

 pyramidata, Sund. Yet. Acad. Handl. 1832, p. 242; Koch, 



Uebers. des Arachn. Svst. erstes Heft, p. 2 ; Die Arachn. B. xi. 



p. 107. tab. 384. fig. 912. 

 I have received specimens of this showy species from Stafford- 

 shire, Shropshire, Northamptonshire, Devonshire, and Middlesex, 

 but I have not observed it either in North Wales or Lancashire. 



XXXIX. — Contributions to the History of the Development and 

 to the Minute Anatomy of the Infusoria. By Prof. Stein of 

 Tharand*. 



[With a Plate.] 



I. Development of Vorticella microstoma, with Comparative Re- 

 marks upon the Mode of Development of the Gregarinidse. 



Tx a previous essay f I have shown that all Vorticellinas at an 

 earlier or later stage of their development become encysted, by 

 drawing in their ciliated disc and contracting their bodies into a 

 ball ; at the same time secreting around themselves a gelatinous 

 mass which solidifies into a firmer elastic covering. Very com- 

 monly a Vorticella will become encysted while still adherent to 

 its stalk, but in that case the stalk soon dies away and disappears, 

 a process which is first indicated by the breaking up of its con- 

 tained muscular band into single portions. More frequently, 

 however, the action of a circlet of cilia developed close in front of 

 the hinder extremity of the Vorticella, detaches it from its stalk, 

 and it becomes encysted while freely swimming. 



The Vorticella thus inclosed gyrates rapidly, and in exceptional 

 cases still appears provided with its posterior circlet of cilia, 

 though, in the majority of cases, this falls off as soon as the 

 encysting substance is excreted. 



The body of the Vorticella inclosed within the cyst always 

 changes subsequently into a globular closed vesicle, which is 

 perfectly homogeneous in its interior, incloses the unchanged 

 band-like nucleus, and possesses besides a round cavity filled 

 with fluid ; the last however no longer changes its capacity like 

 the contractile space of the free animal to which it corresponds, 

 but appears always as a drop of one and the same size. In an 

 appendix to my earlier communication I further stated, that the 



* From Siebold und Kolliker's Zeitschrift, B. iii. H. 4, 1852. 

 t Wiegmann's Archiv, 1849. 



