248 T. W. Engelmann on the Infusoria. 



Stylonychia histrio), it should never be known to enter ? It is 

 moreover very doubtful if such beings as the acinetiform em- 

 bryos of Stylonychia or of Paramecium are so organized as to be 

 able to penetrate their bodies from without. Their structure, 

 indeed, teaches to the contrary; for their soft, weak tentacula 

 are not calculated to penetrate the resistant cuticle of Stylonychia 

 or the thick wall of Paramecium with its contained acicular 

 bodies (trichocysts or thread-cells of Allman), and to hollow out 

 a wide canal such as we meet with in those Infusoria. On the 

 other hand, there are direct observations opposed to this hypo- 

 thesis. Thus, Engelmann recounts several instances in which 

 small Acinetse have affixed themselves to Infusoria and with- 

 drawn their contents by the agency of their tentacula, but have 

 in no degree bored through their integuments. Again, the 

 uniformity always met with in the structure and contents of the 

 embryonic globules is remarkable. In these particulars they 

 exactly resemble those of VorticeUina, the non-parasitic character 

 of which is unquestioned. On the contrary, the substance of 

 the smallest Acinetse is dissimilar; for this, instead of being 

 clear, homogeneous, and destitute of granules, is highly granular, 

 cloudy, and occupied or discoloured with absorbed nutritive 

 material. Lastly, the circumstance is to be noted that the 

 animalcules with which such acinetiform beings are connected, 

 are actually at the time concerned in the development of germs ; 

 and the rule is, as Stein pointed out, that acinetiform embryos 

 are found in most or in all the examples of a species existing in 

 the same fluid — a fact which also holds good with respect to the 

 phenomenon of conjugation. If due weight be allowed to these 

 various considerations, the opinion that the acinetiform beings 

 ill question are really extraneous parasitic Acinetse cannot with 

 propriety be maintained. 



Stein was the first to collect facts relative to the development 

 of the embryonic corpuscles of Stylonychia Mytilus, by showing 

 the conditions and changes of the nuclei and of the nucleoli. 

 Among numerous examples of individual animalcules containing 

 several embryonic corpuscles, only a few presented the two nor- 

 mal nuclei, with either no nucleolus at all, or a single one. In 

 by far the greater number, the nuclei were replaced by three or 

 four, rarely six, oval or sometimes round bodies, and from two to 

 four nucleoli of larger size than in the ordinary specimens of the 

 species (PI. III. fig. 9). Sometimes three or four nuclear bodies 

 were present but no nucleolus. The nature of two of these 

 spherical or oval bodies having the widest dimensions is in all 

 probability that of nuclei, whilst the rest may be considered 

 embryonic corpuscles. These last do not seem always to origi- 

 nate in the same fashion : thus, in some cases, the nucleus is 



