422 MARGARET ROBINSON. 



important it is also the first to appear in the embryo, and 

 apparently functions before there is any sign of a gland in 

 the second maxilla. I must add that I have found antennary 

 glands in two stages which are more advanced than Stage F, 

 and maxillary glands in one of those stages. There is no 

 sign of degeneration in the glands of the adult as compared 

 with the glands in those late embryonic stages. 



It seems to me that these facts about the excretory glands, 

 if they show anything at all as to the systematic position of 

 Neb alia, point rather to its having come off from the original 

 Crustacean stem (from a form in which both glands were 

 equally developed) before either the Entomostraca or the 

 Malacostraca, than to its being descended from either a 

 primitive Phyllopod (Entomostracan) or a primitive Malaco- 

 stracan. 



Genital Cells. — In the thoracic region close to the 

 hepatic outgrowths there is on each side, lying almost 

 between the outgrowth and the mesenteron from which it 

 has arisen, a small group of three or four mesoderm cells 

 (figs. 63, 64). Nusbaum (1887) found what he considered to 

 be genital cells in this place in a similar stage in My sis, 

 though he somewhat unsatisfactorily traced them from the 

 abdomen to this position, and considered them to be ecto- 

 dermal in origin. 



Wagner (1894) states that in My sis the genital cells 

 appear very early as lateral outgrowths of Bergh's (1803) 

 "entoderm disc," and that they travel from a ventral to a 

 dorsal position, which last they reach at a very late stage, 

 having on the journey become surrounded by a layer of flat 

 mesoderm cells. It can be seen that neither of these authors 

 is very convincing as to the origin of the genital cells in 

 My sis, and therefore it is with much hesitation that I suggest 

 the possibility that these cells are genital cells. In my figure 

 they certainly appear to be mesodermal, though they are 

 darker, and more granular, as well as slightly smaller than 

 the other mesoderm cells. If they are not genital cells they 

 may possibly be future connective-tissue cells. 



