620 The American Naturalist. [July, 
anus (a) opens in Diplosoma, as in Appendicularia, independently by 
itself; hence, the anus does not share with the branchial basket the 
phenomenon of occasional regeneration, but persists throughout life. 
In one individual, then, such as is shown in the accompanying diagram, 
there exist five openings, viz., the old incurrent pore (i”), the old 
excurrent pore (e”), the young incurrent pore (i’), the young excur- 
rent pore (e’) and the permanent anus (a). 
This regeneration of a complete organ, not as a result of artificial 
mutilation of the organism, nor as the result of the removal of any 
part, but as a result of a normal physiological process is very remark- 
able. Mr. Oka thinks it similar to certain phenomena common in the 
vegetable kingdom.—-(Translated and abstracted by Dr. Watase, 
Clark University.) 
The Development of the Teeth of Man.—Dr. Carl Röse has 
studied the development of human teeth and comes to the following 
conclusions.’ The first trace of the primary dental ridge appears 
simultaneously (34-40 days) in both jaws. It is in section a semi- 
circular ingrowth of not yet differentiated cells of the epithelium of 
the jaw. It appears at the same time with Meckel’s cartilage. At 
about 48 days (17 mm) the primary dental ridge splits into two ridges 
lying at right angles to each other. Of these the one going vertically 
into the jaw is the labial groove ridge, the other, going horizontally into 
the jaw, is the true dental ridge. The deepest layer of the epithelium 
is of high cylindrical cells. The labial groove ridge continues to grow 
‘ deeper while its upper layer becomes resorbed, thus giving rise to the 
furrow between the lip and the jaw, the process beginning at the mid- 
dle and extending each way. The slight dental groove which runs 
along the line of the union of jaw epithelium and dental ridge is at — 
first on the outer surface of the jaw and gradually wanders in a spiral 
line over the jaw to the posterior surface, the middle advancing more 
rapidly than the sides. 
The dental ridge which at first was horizontal changes its position 
as a result of the growth of the milk teeth, and becomes more and 
more vertical. Its free edges become produced into undulatory out- 
growths, ten in number, which become spherical and form the first 
anlagen of the milk dentition. At the tenth week (embryo of 32 mm 
length) there begins simultaneously, or in quick succession, the push- 
ing in of the papillz into these outgrowths, and these connective tissue 
1Arch. f. mikr. Anat. xxxviii, 447, 1891. 
