56 SYNOPTIC COLLECTION. 



Protozoa the Stentor divides obliquely instead of trans- 

 versely or longitudinally. This is in accordance with the 

 spiral structure of the Infusoria. Just above the mucilag- 

 inous sheath the lateral line of cilia is seen to curve spi- 

 rally ; this marks the spot where a future zoon is to arise 

 by fission. The newly formed zoon sometimes remains 

 with the parent, producing a small colony. 



Gruber 1 ascertained by experiment that division of 

 Stentor took place in most cases at intervals of two days, 

 that daughter zoons divided into granddaughters in the 

 second day after their separation, and granddaughters in 

 another two days into great granddaughters, and so on. 

 In 42 out of 56 cases division took place on the second 

 day after the preceding one. This mode of reproduction 

 is not the only one peculiar to Stentor. A further differen- 

 tiation in the process of fission is observable. The 

 nucleus develops germs or embryos which, becoming 

 detached from it, leave the body of the parent and swim 

 freely about. Such embryos are represented by figs, i 

 and 2 in PI. 55. 



We will now pass to a fixed colonial form of the Infu- 

 soria. The student of nature may find keen enjoyment in 

 the study of the beautiful bell Vorticellidae. These Pro- 

 tozoa are characterized by marked specializations of struc- 

 ture. The protoplasm of which the bell-shaped body is 

 made has become differentiated into three parts, the cu- 

 ticle, ectosarc, and endosarc. Furthermore, the ectosarc 

 has undergone a change whereby the outer portion has 

 become converted into a muscular layer which, according 

 to some authors, extends into the stem, forming the highly 

 contractile spiral axis. The digestive system has become 

 developed so that there is not only a mouth opening but 

 a distinct tube-esophagus leading downward into the 

 body. At the mouth opening this tube flares, and the 

 enlargement is often called the vestibule, while the COn- 



naturforsch. Gesellsch. Freiburg i. B., I, 1886, Heft 2. 

 Engl. transl, Ann. and Mag. Nat. Hist., (5), XVII, 1886, p. 473. 



