v '"' '•' Eitter-Davis.—JEiiteropneusta. isi 



To the interesting question that naturally arises as to whether 

 the stomach carries on digestion at the same time that it is 

 secreting the blastoeoel mass we are not able to give a 

 definite answer. It is certain that practically nothing in the 

 way of food is found in the stomachs of any of the many 

 preserved specimens we have examined; but it is likewise true 

 that one may readily observe material in the stomach of the 

 living larvae, though we have never seen it in any considerable 

 quantity. We are of opinion that the animal is but little 

 dependent upon food from outside sources during larval life, 

 and that the gastric cells engaged in secreting the blastoeoel 

 mass are not concerned at all with digestion during this period. 

 We have pointed out that not the entire stomach is devoted, in 

 equal measure at least, to the secreting, and it is easy to conceive 

 that those portions not so engaged, and particularly the iutes- 

 tinal wall behind the stomach, may perform the digestive function 

 to the limited extent that is demanded. 



Coincidently with the thickening of the stomach wall and its 

 change of function as metamorphosis comes on, there takes place 

 a narrowing of the interval between the ectoderm and the endo- 

 derm, and diminution, probably through resorption, of the 

 blastoeoel mass. 



As we are now sure that the specific gravity of the tornaria 

 is inversely proportioned to the quantity of the blastoeoel mass, 

 we can hardly escape the conclusion that the mass is produced 

 for the purpose of diminishing the specific gravity of the animal, 

 and so must itself be somewhat lighter than protoplasm. The 

 question, then, of what the physical and chemical properties of 

 the mass are becomes one of considerable interest. We have no 

 information beyond that already possessed on the point. Morgan 

 '!»4, states that "so far as microscopic examination of dead 

 material goes, it shows that the fluid is much denser in the older 

 stages." Our observations on the present species do not confirm 

 this. But the nature of the mass needs more careful study than 

 it has yet received. 



The question of the duration of the climactic period is our of 

 interest. Judging by all the evidence we have, both from 

 the observations of others and of our own, on aquarium kept 



