T. W. Engelmann on the Infusoria. 247 



To Stein^s account of the conjugation of Stylonychia Mytilus 

 Engelmann adds that in one instance two individuals were co- 

 herent by their posterior extremities, and that the two varieties 

 of conjugation noticed in the other species above described 

 occur likewise in this one. 



The embryonic development observed by Stein also fell under 

 the notice of Engelmann. In 1859 he found specimens con- 

 taining embryonic corpuscles ; but it was not until the autumn 

 of 1861 that he met with examples which illustrated a further 

 phase in their history. These latter were individuals of medium 

 size, and mostly contained but one large embryonic globule, 

 placed between the two nuclei, close behind the angle of the oral 

 aperture. Placed over it, on the ventral aspect of the animal, 

 there always existed an elliptic or rounded opening, of variable 

 size, which was the outlet for the escape of the mature ovum. 

 On one occasion only was an elongated and rounded dorsal 

 aperture found, in addition to the abdominal foramen just named, 

 and serving, like it, for the escape of the embryos. The act of 

 birth was several times witnessed : sometimes the embryonic 

 globules escaped as such, at others they developed tentacles and 

 assumed the acinetiform figure as usually described. The sub- 

 sequent history of the embryos is unknown to Engelmann; 

 however, he does not believe in their immediate transition to the 

 ordinary form of Stylonychia ; for the smallest examples of the 

 species are more than ten times the length of the largest embryos, 

 and he is therefore disposed to accede to Stein's view, that an 

 " alternation of generation '^ takes place. 



Engelmann protests strongly against the doctrine recently 

 promulgated by Balbiani, that the acinetiform beings seen to 

 emerge from the interior of various Infusoria, and generally held 

 to be their embryos, are nothing less than parasitic Acinetse 

 {Sph(jerophrya of Claparede), which have previously made their 

 way into them. If this were the case, it would be difficult to 

 explain why the Acineta should always penetrate Stylonychia 

 Mytilus, for example, at the same spot ; for the oviduct is con- 

 stant in position, and the integument of the animalcule of con- 

 siderable firmness, particularly at the part perforated. Balbiani 

 indeed figures a Stylonychia Mytilus with three dorsal apertures ; 

 but such a specimen Engelmann has never encountered, in more 

 than a hundred individuals examined by him containing em- 

 bryonic corpuscles. Is it likely that a parasite should always 

 penetrate at one spot in Stylonychia Mytilus, whilst in other 

 Infusoria, as, for example, in Paramecium aurelia and Urostyla 

 yrandisj which have several oviducts, it should pierce at several 

 points ? Why, again, should the supposed parasite bore its way 

 into some species, whilst in others, even those closely allied (as 



