LINNEAN SOCIETY OF LONDON. Xvii 



He also describes, under the name of Polykricos Swartzii, a new- 

 Infusorium which he frequently found in the fiords of the south 

 coast of Norway and in the Gulf of Kiel, and which he regards as 

 especially interesting, from the fact that, with a true infusorial orga- 

 nization, it contains, irregularly distributed in the outer layer of the 

 body, numerous capsules indistinguishable from the true Coelenterate 

 thread-cells. These bodies, however, are never included in a special 

 investment; and he justly regards their presence as affording no 

 argument against the unicellular nature of the Infusoria. He lays 

 it down as a probable distinction between the trichocysts of the In- 

 fusoria and genuine thread-cells, that the former have the power of 

 ejecting their contained filament from both ends of the capsule ; 

 while we know that in the thread-cell it is only one end which gives 

 exit to it. This double emission of a filament appears to have been 

 observed by Biitschli in the trichocysts of a large Nassula ; but the 

 distinction is certainly not a generally valid one. There is no 

 doubt that in the majority of cases the trichocyst emits its filament 

 from only one end of its capsule, exactly as in the thread-cells of 

 the Coelenterata ; and it is hard to see in what respect the bodies 

 noticed by Biitschli in his Polykricos Swartzii essentially differ 

 from true infusorial trichocysts. In conclusion he declares himself 

 strongly in favour of the uuicellularity of the Infusoria. 



The reproductive process was lately followed by myself through 

 some of its stages in a very beautiful Vorticellidan * obtained abun- 

 dantly from a pond in Brittany, The zooids which form the colonies 

 in this Infusorium are grouped in spherical clusters on the extremi- 

 ties of the branches. They present near the oral end a large and 

 very obvious contractile vesicle, and have a long cylindrical nucleus, 

 curved in the form of a horseshoe. In the internal protoplasm are 

 also imbedded scattered green chlorophyl-granules. No trace of 

 the so-called nucleolus was present in any of the specimens ex- 

 amined. 



Among the ordinary zooids there were usually some which had 

 become encysted in a very remarkable way, and without any pre- 

 vious conjugation having been noticed. These encysted forms were 

 much larger than the others, and had assumed a nearly spherical 

 shape ; the peristome and cilia-disk had become entirely withdrawn, 

 the contractile vesicle was still obvious, but had ceased to manifest 

 contractions : brownish spherical corpuscles with granular contents, 

 probably the more or less altered chlorophyl-granules of the un- 



* British Association Reports, 1873. 

 LINN. PBGC. — Session 1874-75. a 



