424 MARGARET ROBINSON. 



lies in the development of the brain with its large central 

 mass of nervous tissue (Nusbaum, 1889). There is also a 

 likeness in the early stages of the development of the eyes, 

 assuming that the proliferation in My sis represents the 

 invagination in Nebalia. If tlie cells mentioned above be 

 indeed genital cells, there is still another point of resem- 

 blance in the development of the genital organs which in 

 the adult My sis and Nebalia are very much alike. The 

 accounts of the development of these organs in My sis given 

 by Nusbaum (1887) and Wagner (1894) are certainly not 

 very lucid, but they agree in one point. According to each 

 of these acconuts the cells travel from a ventral to a dorsal 

 position, and this is what the cells shown in fig. 66 will have 

 to do if they be really genital cells. They certainly resemble 

 very closely those shown by Nusbaum in an embryo of 

 My sis. 



It is very unfortunate that we have at present no account 

 of the development of the excretory glands in My sis. I 

 have, in a somewhat circuitous way, found out that its 

 antennary and maxillary glands develop in the order which 

 obtains for these glands in Nebalia. Nusbaum (1887), 

 though he carried his investigations on to late stages in 

 development, says that he could find no trace of excretory 

 glands in his specimens. I have cut sections through two 

 ]\Iysis embryos which, since their genital organs are slightly 

 more dorsal in position than those shown in Nusbaum's 

 figures, I take to be a little older than his latest stages. In 

 each of these I found a well-developed antennary gland, but 

 no true trace of a gland in the second maxilla. 



In a paper on excretion Kowalewsky and Metschnikoff 

 (1889) state that shell glands have been found by Claus in 

 the larva) of Mysidas. Unfortunately I have been unable to 

 verify this assertion, as they give no reference, and, though 

 I have looked through numbers of papers by Claus, I can 

 find no record of the observation. Assuming Claus's obser- 

 vation to have been correct, I am forced to the conclusion 

 that in the embryos, in which I found antennary glands but 



