210 JOHNS HOPKINS UNIVEESITY MORPHOLOGICAL MONOGRAPHS. 



it is present in the embryo before the stolon itself is formed, nor does it 

 give rise to any part of the chain-salpae except their reproductive 

 organs, although it is easy to understand the nature of the large cell 

 which Todarro has seen and mistaken for the " primo germoblastico.^' 



In the lower part of the body cavity in Plate XVII, Fig. 3, which is 

 from a series of sections from an embryo just a little younger than those 

 in which I found the first traces of the stolon, there is an enormous cell, 

 so large that it runs through a number of sections. It agrees closely, 

 both in its position and in its general appearance, with the cell which 

 he figures and describes as a " primo germoblastico," but the study of 

 other embryos at the same stage shows that its presence at this spot at 

 this time is purely accidental. Similar cells are found in other parts of 

 the body at this and other stages of development, but their position is 

 not constant, and careful study shows beyond question that they are 

 migratory follicle cells from the roof of the placenta. They are shown 

 in the figures of Plate XVIII in the act of migrating into the body cavity 

 from the roof of the placenta where they are formed and set free in great 

 numbers, especially in older embryos. As they break down and disap- 

 pear, only a few are found at one time free in the body cavity, but they 

 wander to all parts of it, and there is nothing constant in their position 

 or number. I have never seen one inside of a stolon, but as its cavity is 

 in free communication with the body cavity of the embryo, there is no 

 reason why they should not sometimes be found there, and Todarro's 

 figures show that this is what he has seen. 



In my account of these migrating placenta cells I shall show that 

 they are not derived from the egg-cell, that their function is nutritive, 

 and that they take no part in the construction of the embryo. 



I am therefore prepared to state with perfect confidence that the 

 germinal mass is not derived from one of them. 



According to Seeliger's account (11, p. 17), which will be examined 

 soon, the amoeboid mesenchyma cells of the nucleus wander from it into 

 the cavity of the young stolon and there build up, not only the germinal 

 mass, but the nervous system, perithoracic tubes, and other parts of the 

 chain-salpa3. Salpa pinnata has no true nucleus, and while it may be 

 possible that, in its origin, the germinal mass is an aggregation of amoe- 

 boid blood-corpuscles from the eleoblast, there is no evidence that this 

 is its history. 



At any rate it is not built up from cells which wander into the stolon, 

 for it is present and well defined before the stolon itself is formed. In 



