INTERNAL ANATOMY OF S(^UILLA. 
421 
be described as the extensive invagination of a swollen sac. In 
both cases sections would reveal tubular structures cut across, 
aud it is only by careful reconstruction and examination of 
tlie investing epithelia that the observer can be certain as to 
which type of structure his sections represent. 
Concerning the comparative histology of the maxillary 
gland of Squilla, I must remark that in general it resembles 
that of the antennal and maxillary gland of other Crustacea, 
as reference to the works of Grobben, Rogenhofen, Allen, 
Vejdovsky and others will show. 
As regards the germ-layer origin of the antennal aud 
maxillary glands in Crustacea, it is interesting to note the 
differences of opinion among authors on the subject. For 
instance, my figure of the youngest stage of development of 
the maxillary gland of Squilla closely resembles those of 
Ishikawa ([11], his fig. 92) and Grobben (10), representing 
the eai-ly development of the antennal glands of Atyephira 
and Cetochilus respectively, but whereas Ishikawa states that 
the young gland is ectodermal in origin, Grobben holds that 
it is mesodermal, arisinof as an invao’ination of the somato- 
pleure. Reichenbach (19) held that the antennal glands of 
Astacus are purely ectodermal structures, and a number of 
later authors agree that at least the external part of the 
gland in the Crustacea is of ectodermal origin, e. g. Ishikawa 
(11) believes that the entire gland of Atyephira is ectodermal, 
whilst Lebedinsky { 15 ), Boutchinsky (2) and Waite (23) state 
that the duct and kidney are ectodermal, the end-sac being 
mesodermal. On the other hand, Grobben (10), Kingsley 
(13) and Robinson (20) consider the whole gland to be a 
mesodermal product, but GrobbeiFs statement concerning the 
somatopleuric invagination is certainly difficult to believe, 
since a coelomoduct is formed as an outpushing, not an 
ingrowth, and Robinson^s figures of the first rudiments of the 
antennal gland in Nebalia show that the initial clump of cells 
may just as well be considered ectodermal as mesodermal. 
It must be concluded, I think, that the evidence for the 
ectodermal origin of the duct nnd kidney of the gland is pre- 
