I KIDNEYS tig 
two pairs—the antennary gland, opening at the base of the 
second antenna, and the maxillary gland, opening on the second 
maxilla. These two pairs of glands rarely subsist together in 
the adult condition, though this is said to be the case in Nebalia 
and possibly J/ysis; the antennary glands are characteristic of 
adult Malacostraca! and the larvae of the Entomostraca, while the 
maxillary glands (“shell-glands”) are present in adult Entomo- 
straca and larval Malacostraca, that is to say, the one pair replaces 
the other in the two great subdivisions of the Crustacea. The shell- 
gland of the Entomostraca is a simple structure consisting of a 
coiled tube opening to the exterior on the external branch of the 
second maxilla,-and ending blindly in a dilated vesicle, the end- 
sac. The antennary gland of the Malacostraca is usually more 
complicated: these complications have been studied especially by 
Weldon,” Allen, and Marchal* in the Decapoda. In a number 
of forms we have a tube opening to the exterior at the base of 
the second antenna, and expanding within to form a spacious 
bladder into which the coiled tubular part of the kidney opens, 
while at the extremity of this coiled portion is the vesicle called 
the end-sac. This arrangement may be modified; thus in 
Palaemon Weldon described the two glands as fusing together 
above and below the oesophagus, the dorsal commissure expand- 
ing into a huge sac stretching dorsally down the length of the 
body. This closed sac with excretory functions thus comes to 
resemble a coelomic cavity, and the view that it is really coelomic 
has indeed been upheld. 
A modified form of this view is that of Vejdovsky, who 
deseribes a funnel-apparatus leading from the coiled tube into 
the end-sac of the antennary gland of Amphipods; he regards 
the end-sac alone as representing the coelom, while the funnel 
and coiled tube represent the kidney opening into it. 
Not very much is known of the development of these various 
structures. Some authors have considered that both antennary 
and maxillary glands are developed in the embryo from ecto- 
dermal inpushings, but the more recent observations of Waite * 
on Homarus americanus indicate that the antennary gland at 
1 The Cumacea, Anaspidacea, and certain Isopods possess a maxillary gland 
only. 
2 Quart. J. Micr. Sct. xxxii., 1891, p. 279. 
* Arch. Zool. Exp. (2) x., 1892, p. 57. 
4 Bull. Mus. Comp. Zool. Harvard, xxxy., 1899, p. 152. 
