ON THE DEVELOPMENT OF NEBALIA. 423 



The vitellopliags are mucli reduced in number. They are, 

 in fact, only to be found in the unsurrounded yolk at the 

 front end of the embryo. 



Conclusion. 



Claus's last paper is, among other things, a great summing 

 up in favour of the Malacostracan position of Neb alia. The 

 history of the development, as far as I have taken it, can do 

 little but make his position still stronger. The thoracic limbs 

 are perhaps the most Phyllopod-like feature thatNebalia 

 possesses, and Claus has shown these to be intermediate in 

 character, between those of a Phyllopod and those of the 

 Schizopoda. 



A Malacostracan feature in the development of Nebalia, 

 to which, I believe, notice has not yet been drawn, is the 

 sharpness of definition with which the embryonic stages are 

 marked off from one another. 



Among the Malacostraca the form which appears to be 

 most nearly related to Nebalia is Mysis. The organs 

 which are alike in the adults are alike also in their develop- 

 ment. To begin with external points. The very definite 

 early embryonic stages in Nebalia resemble very closely 

 the early embryonic stages in Mysis, and in both animals 

 the young stay in the brood pouch of the mother till they 

 are practically adult. The brood pouches in the two animals 

 are formed in the same way by spiny outgrowths on the 

 coxopodites of the thoracic legs. 



The peculiar form of gastrulation, the development of the 

 endoderm in Stage B, the subsequent formation of the mid- 

 gut by circumcrescence, and the development of the liver 

 lobes in Nebalia all closely resemble the facts as recorded 

 for Mysis (Nusbaum, 1887, and Bergh, 1893). 



If the heart arises and develops as I have suggested above, 

 then its development resembles that in Mysis more nearly 

 than that in any Phyllopod. Another point of resemblance 



