INTEGUMENT OF NECTURUS MACULOSUS 541 
cous glands larger, abundant, none on the ventral surface.” 
The contradictory statements made by these writers regarding 
the distribution of the glands on the ventral surfaces of the 37- 
and 43-mm. embryos are probably due to the fact that the 
descriptions were based on animals which exhibited individual 
variation in the time of the development of the glands. From 
the meager account given it seems that the mucous glands must 
develop first and that they are limited in very young embryos 
to the dorsal region. I have not had an opportunity of studying 
embryonic material, but the adult animals and the 10-cm. larva 
upon which I worked furnished quite complete series of stages 
in the development of both types of glands. In the larva develop- 
ing glands were numerous. In the adult they were found only 
occasionally. In all of the:material examined no evidence was 
obtained to indicate that the granular glands were derived from 
those of the mucous type, but everything pointed to a separate 
origin and development for each kind of gland. The description 
of the development of glands in the larvae, with the exception of 
Phisalix (’00, ’03), are all essentially alike. Maurer (’95), Ancel 
(02), Nirenstein (08), and Muhse (’09) have found that at 
frequent intervals a single cell in the lower cell layer of the 
primitive epidermis becomes differentiated. Rapid cell division 
follows and a solid mass of cells, the gland bud, is soon formed. 
This group of cells is at first contained in the epidermis and 
produces a bulging toward the dermis. Later the cell mass 
pushes down into the dermis, but retains its connection with the 
epidermis. Soon a lumen arises in the center of the mass, and 
at the point of connection with the epidermis the future duct 
is developed. 
In the adult Necturus the youngest gland found was a bud 
consisting of about twelve cells which lay well within the dermis 
(fig. 17). The arrangement of the cells in the overlying epi- 
dermis was disturbed and open spaces were observed in the 
malpighian layer, indicating an active emigration of cells from 
that region. In this case, the developing gland entered the 
dermis along one of the perpendicular bundles of connective 
tissue. In figure 18 a somewhat later stage than that of figure 
