ON THE DEVELOPMENT OF NEBALIA. 421 



form a space between thetnselves and the dorsal ectoderm. 

 It is much in this way that the heart in the Crayfish arises 

 (Reichenbach, 188(3). 



The Ante n nary Gland. — In the stage with nauplius 

 appendages mesoderm cells can be seen being carried into 

 the appendages as they are folded off from the rest of the 

 bhistoderm (figs. 20 — 22, mes.). In Stage D mesoderm cells 

 can be seen lyiug in the antennte between the two layers of 

 ectoderm, though there is there very little histological 

 difference between ectoderm and mesoderm (figs. 37 — S9,mes.). 

 Still, having traced mesoderm into the antennae and finding 

 no sign of an ectodermal invagination of any kind I have 

 little doubt that the glands which appear at the bases of the 

 second antennae in Stage E are mesodermal in origin. These 

 glands in this stage (F) are in the same condition as in 

 Stage E (figs. 55, 59). There is no duct as yet, nor is there 

 any sign of a gland in the second maxilla. Claus (1889) 

 showed that in the adult Nebalia both glands function, and 

 his observations have lately been confirmed by Bruntz (1904). 

 In the adult the antennary gland is very rudimentary, and 

 that in the second maxilla still less developed. Claus (1889) 

 uses these facts as evidence in favour of Nebalia's belonging 

 to the Malacostraca ; for, he says, that while in Phyllopods 

 the antennary glauds appear first, and function, while the 

 shell glands, if present, are insignificant and functionless, in 

 the adult the auteunary glands have dwindled, and it is the 

 shell glands which function. In the Malacostraca, he 

 continues, the relative importance of these two glands at the 

 different ages is reversed, and in the adult it is the antennary 

 gland which functions while the maxillary gland, if present, 

 is comparatively insignificant. These statements have 

 received further confirmation in Dr. Allen's work on the 

 Nephridia of Decapods (1893). But it seems that logically 

 speaking this piece of evidence, though it certainly helps to 

 remove Neb alia from the Entomostraca, does not help to 

 place it among the Malacostraca; for though in the adult 

 Neb alia the antennary gland is the larger and the more 



