T. W. Engelmann on the Infusoria. 251 



likewise possess a tolerably large nucleolus, usually situated on 

 the concave side of their elongated nucleus. In several new 

 forms described by Engelmann this same organ is found, viz., in 

 Drepanostoma striatum, Chasmatostoma reniforme, Lacrymaria 

 elegans ; some new Oxytrichina, as Pleurotrocha setifera, Gastro- 

 styla Steinii, Uroleptus fragilis, Oxytricha strenua, and O. paral- 

 lela. With less certainty he refers to a nucleolus in Opercularia 

 coarctata, Zoothamnium Aselli, Urocentrum Turbo, and in some 

 other well-known Infusoria. On the other hand, he has con- 

 vinced himself of its presence in all the OxytricTiina known 

 to him, in Euplotes, in Chilodon cucullulus, Nassula aurea, 

 Prorodon teres, Lacrymaria olor, Panophrys flava { = Bursaria 

 flava, Ehr.), Colpidium, Stein {=i Paramecium colpoda), Balantidium 

 entozoon, Paramecium Bursaria, and P. aurelia, Entodinium 

 bursa and E. caudatum, Carchesium polypinum and Epistylis di- 

 gitalis. All Engelmann's attempts to find a nucleolus in Epi- 

 stylis plicatilis have failed ; and he is unable to confirm the 

 existence of one in Blepharisma lateritia, although Balbiani has 

 described it. Nevertheless in one specimen of the species last 

 named he noticed a large sac, placed in front of the nucleus, 

 filled with rigid, motionless, acicular bodies resembling, both 

 before and after the addition of acetic acid, the spermatozoa of 

 Pai^amedum aurelia. He found also other specimens of the 

 same animalcule in which the nucleus was broken up into five 

 or six spherical segments, of homogeneous consistence — an ap- 

 pearance Stein has also noted and figured. 



In one and the same species, among several of the Infusoria, 

 the nucleoli vary in number. A remarkable instance of this fact 

 occurs in Stylonychia Mytilus, in which from two to four nucleoli 

 are present. In Urostyla Weissei from two to eight occur ; and 

 Stylonychia histrio has at one time two, at another four nucleoli. 



The purpose of the slit-like openings in the nucleus, as ob- 

 served by Stein in Oxytrichina and in Aspidisca, is not determined. 

 One supposition is, that they may serve an important end in 

 sexual reproduction by giving passage to the spermatozoa. They 

 are usually arranged quite symmetrically, and are approximated 

 towards each other, or placed at opposite extremities of the nu- 

 cleus. Anomalies, however, occur at times. 



Engelmann remarks on a slit- like aperture in the area of the 

 peristome of Onychodromus, lying obliquely across the direction 

 of the anterior nucleus, and recalls, in connexion with this ob- 

 servation, the presence of a crescentic line described by Stein 

 and Balbiani as dividing the peristome of Stylonychia Mytilus 

 into an anterior and a posterior segment. Balbiani has further 

 remarked the like structure in Trachelius ovum, and imagines 

 that these slits may be structurally connected with the rcpro- 



