1G2 Dr. M. Verworn's Biological Studies of Protista. 



I was able to keep alive for two months in watch-glasses 

 with sea-water in which small pieces of Ulv^e were placed to 

 produce the necessary oxygen. As their shells were not very 

 thick, I succeeded very well with them also in effecting 

 divisions and injuries with the lancet in definite places, in 

 which the uncommon viscosity of the protoplasm alone caused 

 some difficulty. In the PoJystomellce the nucleus is usually 

 situated in the same part, and, indeed, in the neighbourhood 

 of that chamber upon which the youngest chamber is seated 

 externally. In consequence of this we may know beforehand 

 with some certainty whether we shall or shall not liave the 

 nucleus in any separated portion. Of course the portions, 

 after the investigations were completed, were also decalcified 

 with acetic acid and stained with carmine, so that there could 

 remain no doubt as to their containing or not containing a 

 nucleus. 



The divisions or mutilations were performed in the fol- 

 lowing manner. First of all from two to four of the first 

 chambers were removed from some individuals. These ampu- 

 tated chambers showed no phenomena of regeneration, 

 although they remained alive for a long time. In the other 

 portions, however, which contained the nucleus, the irregular 

 broken place was usually repaired again in from three to six 

 days in the following manner : — the protoplasm swelled out 

 in a rounded form somewhat above the spot in question, and on 

 its surface a calcareous layer was secreted (PI. IX. fig. 4). In 

 its form this calcareous layer resembled the outer wall of the 

 youngest chamber of an uninjured Protistan, and showed the 

 typical structure of the shell of a Polystomella perforated by 

 numerous small apertures. The ruins of the tubular system 

 of both sides of the last amputated chamber were not again 

 completed into perfect tubules, but remained in their injured 

 condition, and the newly formed wall had founded itself 

 directly upon them. In one case, however, there were 

 already to be seen upon the outer surface of the newly formed 

 wall the indications of a whole new system of tubules (fig. 5), 

 and this evidently would have been completely developed as 

 soon as a new chamber was founded upon the new wall. 

 The newly formed wall in fact on the two sides, where the 

 tubules are formed in the normal chamber-walls, was perfo- 

 rated by apertures of corresponding size, which were sur- 

 rounded by a low wall, the indication of the future tubules. 



In those individuals in which two chambers were mutilated 

 each chamber did not complete itself separately, but a calca- 

 reous layer was secreted only on the surface of the outer of 

 the two cut chambers. 



