BULLETIN OP THE UNITED STATES FISH COMMISSION. 301 



I have not found a single member of this species in the many diseased 

 or dead crawfish which I have examined. In consequence, it is per- 

 fectly clear to me that it is not this parasite which does the mischief. 

 I will mention some leeches, some Branchiohdella astaci, Odier, and B. 

 parasita, Henle^ as well as some psorospermic corpuscles 0.15 millime- 

 ter [.0059 inch] in length, a few of which were found in the thorax 

 of certain crawfish. By analogy with what takes place in various 

 contagious diseases, some persons have been led to think that a crypto- 

 gamic growth could be the cause of the mischief. But the results 

 reached in following out this hypothesis have been entirely in the nega- 

 tive. Oji the contrary, it is certain that nearly all the organs of the 

 diseased crawfish — the tissues of the heart, the cavity of the stomach 

 and also of the intestines, the nerve ganglia, most of the muscles, the 

 adipose tissue, the gille, &c. — are full of a multitude of little ovoid, cellu- 

 lar substances, which sometimes accumulate in such quantity at cer- 

 tain points that the organs are torn asunder. This accounts for the 

 frequent loss of claws. These ovoid corpuscles measure 0.02 millimeter 

 [nearly .0008 inch] in their longest diameter and 0.013 millimeter 

 [about .0005 inch] in their shortest diameter. They can easily be 

 colored red by picrocarminic acid." 



How do these corpuscles get into the organs of the crawfish 1 This 

 is difficult to explain. We do not find that they make any kind of mo- 

 tion, even when we get them from crawfish which have scarcely 

 ceased to live. It is supposed that these cellules spread progressively 

 in the water during the decomposition of the dead crawfish, and that in 

 this new condition they continue a certain development. "I have no 

 doubt," says Dr. von Linstow, " that they belong to the animal king- 

 dom and to the sub-kingdom of Protozoa, and it is probable that in its 

 perfect state the parasite should be classed among the Gregarinidte or 

 the Amoebea." 



The question of learning whence these corpuscles come, and how we 

 can protect the crawfish from them, remains as j'et entirely unanswered; 

 but a step is taken towards its solution when we discover the enemy to 

 be opposed. Henceforth the problem to settle, as Dr. von Linstow con- 

 tinues, would be, so Dr. Leukart thinks, that of the cultivation of this 

 parasite outside of the organs of the crawfish ; and if its development 

 can be attained under these conditions ^e shall doubtless arrive at the 

 determination of the question by what means and in what manner the 

 parasite finds its way into the tissues of the crawfish. 



When we consider the difficulty there is to distinguish, without the 

 aid of the microscope, the diseased crawfish from those which are healthy, 

 we can ask whether the consumer has not some risk to run from the put- 

 ting up for sale of crawfish which were already somewhat aftected. The 

 reply. Dr. von Linstow afiirms, is that the crawfish, even though diseased, 

 can be consumed without any fear, because the protozoan which causes 



