232 Dr. C. F. J. Lachmann on the Organization of Infusoria. 



has been completely disregarded, was made by Von Siebold*, 

 upon an Infusorium {Bursaria or Opaliyia) living as a parasite 

 in tbe intestine of the Frog : in this he found a number of 

 small embryos in a cavity at the posterior extremity of the body. 

 Embryos were subsequently rediscovered, first by Fockef (whose 

 observations were confirmed and enlarged by Cohn J and Stein §) 

 in Paramecium Bursaria, Focke = Loxodes Bursaria, Ehrbg., 

 then by Eckhardt|| in Stentor pohjmoiyhiis and cceruleus (con- 

 firmed by O. Schmidt^), by Stein** in many Acinetce and in 

 Chilodon, and, although less exactly, by Cohntt in Urostyla 

 grandis. From the observations of Focke and Stein, a division 

 of the nucleus appeared to take place in the formation of em- 

 bryos ; whilst Eckhardt does not refer to this, and Cohn regards 

 its division as improbable. I have been so fortunate as to ob- 

 serve the formation of embryos, not only in many Acinetince, 

 but also in numerous other Infusoria. As the description of 

 these observations, which were for the most part made in con- 

 junction with E. Claparede, would lead us too far, we shall fur- 

 nish this in a separate memoir ; and I only give here the scheme 

 of development, such as we have observed it more or less com- 

 pletely in different cases. 



The development of the embryos takes place in the nucleus, 

 or in a part of it. The nucleus is usually seen first of all to 

 divide into two or more parts, when the same processes take 

 place in one or several of these parts, which in other cases occur 

 in the undivided nucleus. The nucleus is usually roundish or 

 longish, or even (as in many Vorticellince and Stentor) much 

 elongated and band-like : it is enveloped in a peculiar mem- 

 brane, as Stein has proved, and generally presents a homoge- 

 neous or finely granular appearance ; it appears constantly to 

 enclose a cavity surrounded by thick walls (the substance of 

 the nucleus), sometimes {Chilodon) containing a smaller body, 

 the nucleolus, which in other species is situated close to the nu- 

 cleus. Upon or in the wall of the nucleus or one of its products 

 of division, we now sometimes perceive small round globules, 

 which increase in size, finally acquire a contractile vesicle, and 

 become converted into embryos ; these at last become furnished 

 with cilia, escape out of the parent animal, and swim about 



* In his Memoir upon the development of Monostomum mutabile, in 

 Wiegmann's Archiv, 1835. 



t Amtlicher Berieht der Natnrforscherversammlung zu Bremen, 1844, 

 p. 110. 



X Siebold and Kolliker's Zeitschr. iii. p. 277. 



§ Op. cit. supra. 



II Wiegmann's Archiv, 1846. 



II Froriep's Notizen, 18-il9, p. 7- 



** L. c. supra. ft L. c. supra. 



