THOMPSON : A PARE TIIALASSINID. 
11 
The abdominal musculature is the same as that of an adult Mac- 
ruran. A green gland is found in all stages, but in the first stage 
its lumen is limited and the cells which make up the wall resemble 
somewhat the undifferentiated cells which occur in all parts of the 
body during larval development. In the succeeding stages, how¬ 
ever, the histology which characterizes this organ in Crustacean 
larvae becomes apparent; i. e., the cell boundaries are indistinct, 
the protoplasm is homogeneous, granular, and stains darkly, and the 
nuclei are large with a well marked reticulum. Diverticula arise 
in the fourth stage. A small shell gland (pi. 3, fig. 41, sh g) is also 
present throughout the preadolescent period. 
The Naushonia young have one very remarkable internal struc¬ 
ture (pi. 3, fig. 41, vg). This is a cluster of cells, frequently with 
a smaller accessory group at one side, which lies beneath the nerve 
cord, partly in the second maxilla and partly in the first maxillipedal 
segment. Its position is marked externally by an inconspicuous 
swelling. The cells which compose this “ gland ” are arranged 
radially. There is apparently an indefinite central lumen but this 
shows no opening to the exterior. An opening may exist, however, 
as Claus (’ 84 ) figures an orifice in the similar structure which he 
describes for the young of an Adriatic Thalassinid, Calliaxis. The 
cells have a granular cytoplasm which does not stain deeply nor 
blacken on treatment with osmic acid; their nuclei are peripheral. 
As no distinct hypodermal cells can be seen in the region, the organ 
is probably a modification of the hypodermis. We have no clue 
to its function, although it somewhat resembles the glands with 
radially arranged cells which lie in the labrum and around the 
oesophagus of many Crustacean larvae. It seems as if this struc¬ 
ture must rank with the asymmetrical mandibles as a distinction 
between the young of Naushonia and the young of most Decapods. 
Adolescent Development. 
The lack of any approach to the adult form during the later pre¬ 
adolescent stages, together with the close resemblance that exists 
between adolescent and adult stages, makes the metamorphosis at 
the close of the mysis phase very striking. Moreover, the first 
adolescent is only six millimeters long, while the preceding stage 
