246 PROFESSOR SMITT. 



BaciVariacea, two others, namely, a water-like fluid sub- 

 stance, and oil globules differing in size. These latter occur 

 swimming freely in the cell, but abound upon the inner 

 surface of the plasm-sac. In consequence of their strong 

 refractive power, they strike the eye at once, and are changed 

 into a black colour by the use of osmic acid. As they 

 readily combine, they have no skin. The author's experience 

 confirms the observation of Luders, that in proportion as 

 the oil abounds, the cells have suffered from the want of 

 pure water. The appearance of the larger oil-globules is 

 a sign that the cell has attained its full maturity and 

 exhausted its resources. 



The oil- globules afford a means of answering the question 

 whether the cell-contents are of a watery or of a gelatinous 

 consistency. In favour of the former view. Dr. Pfitzer 

 refers to the fact that very weak acid produces an immediate 

 shrinking of the plasm-sac, as also to his observation that the 

 oil-globules can be moved about with facility, which could 

 not happen if the surrounding matter were of a gelatinous 

 nature. The opinion of our author on this subject is 

 corroborated by Focke, who discovered that the oil-globules, 

 in consequence of their light specific gravity, accumulate on 

 the upper surface of the cell, and change their position in 

 case the frustule is turned upside down. 



Remarks on Dr. Nitsche^s Researches on Bryozoa. 

 By Professor Smitt. 



In the ' Zeitschrift fiir wissenschaftliche Zoologie,' Bd. vi, 

 Hft. 4, Doctor Hinrich Nitsche has published his " Beitrao-e 

 zur Kentniss der Bryozoa," of whom you already, in April, 

 1871, had received and published an extract — " On some 

 Interesting Points concerning the Mode of Reproduction of 

 the Bryozoa." In these excellent papers you will find a critique 

 of my views on the subject, as well as very good additions to 

 my observations; but I am sorry to find that the distin- 

 guished doctor in many points has mistaken my meaning 

 and overseen my statements, without doubt because of the 

 difficulties of the language. 



Thus I never have said, and could not think any one should 

 impute to me such a thought (' Zeitscbr.,' 1. c, p. 446), that 

 the zooecia in the common-bud differentiate themselves cen- 

 tripetally from the peripheral margin of the bud. Any 



