126 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
tinet in Moina as in Penilia but more or less mixed with the meso¬ 
derm. Only later the central cells of this mes-entoderm separate 
themselves from the main mass to form a cylindrical and solid rod 
of entoderm which later obtains a lumen as described for Penilia. 
The cells Ivins: outside of this are the mesoderm. 
%j O 
Tiie Shell-Gland. 
The shell-gland of the adult Penilia is a marked departure from 
that organ as seen in other members of the group. Instead of 
being long, tubular, and coiled, it is almost circular in outline. It 
is composed of from six to ten large cells described elsewhere. 
The shell-gland has its origin in the mesoderm in Penilia. Certain 
cells in the mesoderm on either side of the digestive tract just 
above the second maxillary segment begin to enlarge. These cells 
have larger, darker staining nuclei than the surrounding mesoderm 
cells, and they soon show a spherical arrangement. These cells con¬ 
tinue to enlarge until they form a solid sphere almost as large 
as the organ of the mature animal but with no lumen present. 
Later, but before they have assumed the definite histological struc¬ 
ture of the adult, they appear around a lumen with an opening 
to the exterior through the ectoderm. Grobben also confirms the 
mesodermal origin of this gland for Moina, but the different shape 
and histological character of the glands of the adults make their 
rudiments in the respective embryos somewhat different. Kingsley 
finds the homologous gland of Crangon to be of mesodermal 
origin and that later in the development it acquires an ectodermal 
opening to the exterior. Reiclienbach in his work upon Astacus 
and Isliikawa in his work on Atyephira both find this gland of 
ectodermal origin and the mesoderm plays no part in any stage of 
its development. 
The Cervical Gland. 
Throughout the arthropods one or more glands are formed in 
the neck and head region at various stages in their development. 
Different investigators have given the same structure different 
names such as cervical gland, neck-organ, dorsal gland, and 
midusium. In Penilia a cervical gland is present here in the 
