684 Transactions of the Society. 



obtain similar results on other objects, but less distinctly. Shortly 

 afterwards, the classical works of Engelmann, and more recently 

 of Merkel, whilst confirming the complicated muscle structure and 

 further by investigating the relations of the elementary particles 

 before and after the contraction, have closed the question for some 

 time to come. 



If after this Prof. Abbe's objection against muscle sculpture in 

 general is tacitly accepted as set aside, then, in view of the fact 

 that among the numerous diatom investigators hardly one has 

 seriously occupied himself with the structure of diatoms, it becomes 

 all the more difficult to controvert Abbe's views since I am the 

 only one to whom falls the task of doing so. I must not forget, 

 however, that Dr. Altmann has every now and then vindicated my 

 views against Abbe.* 



It would lead too far away from our subject if I were here to 

 enter on the merits of their difierences ; he who takes an interest 

 therein should read Archiv fiir Anat., 1880, pp. Ill et seq. In 

 our present discussion it is enoijgh that all my results obtained 

 hitherto are in direct contradiction to Abbe, Any one desirous of 

 arriving at a definite opinion can inform himself by my diagrams 

 and photographs, or by repeating my experiments. Suppose the 

 student in microscopy investigates the sculpture of an object which 

 is unknown to him, limiting himself to the surface-view only, say, 

 for instance, the Pleurosigma valve, it is certain that he will be 

 unable to solve various doubts, and in this I quite agree with 

 Prof. Abbe ; he will not be able to decide whether certain lines 

 are raised or depressed, whether they are situated inside or outside ; 

 on this subject microscopical literature records the most unfruitful 

 squabbles. But if the investigator examines the object by sections 

 and makes casts of the surface, and makes use of the staining 

 processes, &c., and finds, for example, exactly at the place of a 

 previously doubtful line a projection, then it becomes immaterial to 

 him whether the Microscope deceives us in the surface- view and 

 gives images which do not correspond to reality. If the Micro- 

 scope deceives us in one case, then it also does so in others. The 

 change in the methods of investigation puts us in the position to 

 find out the truth. As soon as the investigator takes the result 

 obtained by all his methods and compares it with the surface- 

 image, he will in most cases have answers to all his questions 

 without being obliged to enter into the depths of the difiraction 

 theory. I observed these maxims in my work on Pleurosigma 

 sculpture, and I hold to them at the present day. 



To this cannot be opposed the fact that one can obtain by 

 artificial means images like diatom markings, and such difiraction- 



* Personally I do not know Dr. Altmann, therefore I take this opportunity 

 to tender him mv best thanks. 



