ORIGIN OF GASTRIC GLANDS OF ACANTHIAS 357 
ence of gland rudiments have changed this simple uniform 
condition. No longer are the epithelial cells arranged in the 
form of a single continuous row in embryos 137 mm. long. On 
comparing figures 2 and 3, it is evident that as soon as a gland 
rudiment is well marked out in the epithelium (fig. 3) it forms 
a bottle-like plug. The lower expanded portion of the plug 
tends to press upon the neighboring epithelial cells, thus crowd- 
ing them closer and closer together. This lateral displacement 
of the epithelial cells proceeds unhampered, as they are not 
anchored fast by a basement membrane, but may extend freely 
down into the underlying mesodermic tissue.!. As a result of 
compression exerted by the expanded part of the bottle-like 
plug of the gland rudiment, or for a lack of space, the epithelial 
cells are closely approximated at their bases. Since the distal 
parts of the epithelial cells have not been affected by the mechan- 
ical forces involved in the compression phenomena, it naturally 
follows that the portion of epithelium intervening between two 
gland rudiments takes on a fan-shaped form in cross-section 
(fig. 3). This peculiar arrangement of the epithelial cells, as 
compared with the simple uniform condition in the earlier 
stages, is maintained in the later stages. 
D. Subsequent history of the gland rudiments 
The subsequent history of the gland rudiments will now be 
considered in detail. Acanthias embryos 137 mm. long furnish 
very favorable material for such considerations. At this stage 
many of the gland rudiments are undergoing a great change in 
their length; their constituent cells are growing out into the 
mesodermic tissue. During the course of a very short period 
of time every gland rudiment will have elongated and burrowed 
its way into the underlying tissue. 
Figure 4 represents one of the so-called epithelial outgrowths 
in the gastric epithelium of an Acanthias embryo 137 mm. 
1 Hopkins (95) believes that a basement membrane does not exist in the 
ganoids. According to Edinger (’77), fishes possess no basement membrane, 
but the epithelium borders directly upon the underlying tissue. 
