1893.] Embryology. 487 
per, Maurice and others, that the mantle of this ascidian should be 
regarded as an epidermis-like structure, a thickening of the ectoderm 
with large amounts of intercellular material between the ectodermal 
cells. 
On studying sections of this larva, however, he obtained evidence 
that mesodermal cells migrate out through the epidermis of the larva 
into the thick hyalin cuticle or secreted mantle matrix, and thus supply 
mesodermal cells as the fundamental cells of the mantle. 
These migrating cells the author would regard as a sort of phagocytes 
and imagine to have a primary function in destroying the injurious 
parasites, bacteria, etc., that would easily lodge in the secreted mantle 
matrix. 
In the same paper there is an interesting account of the degenerative 
changes that the tail of the larva undergoes when free life is given up. 
After peculiar histological transformations in the notachord and mus- 
cles of the tail, these cells and the epidermal cells pass into the body. 
The last of the tail is drawn in by an actual hollow invagination that 
forms a closed vesicle in the body. The ultimate changes in the mus- 
cle cells are accompanied by the activity of clusters of phagocyte-like 
mesoderm cells. 
