Blood-corpuscles of Tridacna. 449 



Sill.* I am not acquainted witli other cases of the same 

 kind. But, at any rate, the Algal vegetation in the system 

 of blood-lacunfB in the mantle of Tridacna proves that there 

 can be no question of any " current " of blood in tliem worth 

 mentioning. However, it cannot be denied that Algaj 

 (always supposing them to be such) must yield a very valu- 

 able enrichment of any animal blood, as the oxygen which 

 they develop under direct exposure to light must be immedi- 

 ately absorbed by the blood-plasma, and so benefit the animal 

 to a great extent. That there can be no question of even a 

 temporary or partial nourishment by the vegetable symbionts 

 in the case of an animal so large and requiring so much 

 nutriment as a Tridacna is a matter of course, even if this 

 theory, set up by G. Entz and Brandt, were not to be re- 

 garded as already seriously shaken. 



Some minor observations made in the course of the above 

 investigation, but which have no other connexion therewith, 

 may here find a place in conclusion. One of my observations 

 relates to the blood-corpuscles. In my preparations I found 

 these always fixed in a peculiar manner. The protoplasm 

 had distinctly separated into two different constituents — a 

 perfectly hyaline part in which the nucleus was always 

 situated excentrically, and a "■ protoplasmatic " part, which 

 showed a very marked fibrous coagulation. It was remark- 

 able that in all three of my Tridacme, which had been treated 

 with quite different reagents, namely chromic acid, alcohol, 

 and osmium, the blood-corpuscles appeared altered in this 

 manner, and, indeed, in each preparation the whole of them 

 without exception, not only those of the deeper layers of 

 tissue, but also those belonging to the subepithelial layers, 

 which one would have supposed must have been killed and 

 fixed almost instantaneously by the reagent employed. I am 

 at present quite unable to offer any explanation of this peculiar 

 phenomenon. 



The following peculiarity of the blood of Tridacna may 

 have more interest. I believe that the only known formed 

 constituents are the ordinary amoeboid blood-cells. But in 

 Tridacna I succeeded in detecting, although very sparingly, 

 a second very characteristic cell-element of the blood. These 

 were rounded or oval, lobate, or otherwise irregularly formed 



* Silliman, " Beobachtungen liber die Siisswasserturbellarien Nord- 

 amerikas," iu Zeitschr. f, wiss. Zool. Bd. xli. p. 62. 



