542 The American Naturalist. [June, 
become free, and as belonging to the organisation of the animal. They 
have thought that all the transition stages between the simple ciliated 
epithelial cells of the intestine and the free urnes may be found. 
Kunstler and Gruvel assert that the bodies have a different history, 
and, if the correctness of their observations be granted, we must give 
up the conclusions that we have supposed well-founded and return to 
the ideas of Vogt and Young and Fabre-Domerque and consider the 
bodies as autonomous organisms. But, if they are such, the question 
arises, What can be their history in the eavity of the young Sipunculus, 
how did they gain entrance, and from whence did they come? 
According to these authors the urne is the final stage in a series, and 
represents the form of the organism or element that is most common. 
This element becomes flattened and enlarged in its ciliated: region, 
while its hyaline vesicle looses its spherical form. As a result of the 
change of form, there is produced a large disc having waving move- 
ments. While these changes are taking place there appear in the lower 
side of the disc numerous cellular elements that soon become free and 
function as reproductive bodies. 
The latter have been known under the name of amcebocysts. They 
are generally provided with numerous long and thin pseudopodia, and 
sometimes structures resembling undulating membranes. Their granu- 
lar protoplasm contains two bodies, one colorless, the other dark, that 
resemble nuclei. In the course of growth the colorless body increases 
in size faster than its dark companion, and finally escapes from its con- 
taining element. There is thus left an element having pseudopodia, and 
containing a small dark colored body. The pseudopodia become more 
numerous and smaller, and somewhat later some of them become 
flagellate at the peripheral zone. They are then minute urnes that 
soon, by the simple process of growth, become urnes of the normal size. 
Besides the urnes and their reproductive modifications, there may be 
found, in the liquid of the body-cavity of Sipunculus, certain bodies 
that, evidently for want of a better term, the authors call enigmatic 
vesicles. To a certain extent, these resemble the urnes. By the sim- 
ple process of fission they produce large cellular plaques composed of 
two layers of cells or elements. An application of staining reagents to 
these brings out marked differences. Some of the elements stain readily 
and deeply, others appear to be scarcely stainable. 
In the course of time the clear elements become isolated, repeat the 
process of division and in their turn produce plaques. The other ele- 
ments give rise to buds that are nucleated and provided with a hyaline 
vesicle. The attaching pedicle of the bud becomes greatly lengthened 
and finally breaking away the bud becomes a free, large ameboid body, 
