ON THE DEVELOPMENT OF NEBALIA. 389 



descended from the Pliyllopoda through Nebalia, Boas 

 (1883), while considering Nebalia as transitional, is careful 

 to point out that, in his opinion, this is not a case of direct 

 descent. " Sie steht nicht auf dem geraden Weg von den 

 Pbyllopoden zu den Malacostraken, sondern etwas seitlich." 

 He considers Thysanopus (an Euphausid) to be the most 

 primitive Malacostracan, and the nearest to Nebalia, but it, 

 like Nebalia, does not lie on the direct route from Pliyllo- 

 poda to Malacostraca. His views are founded mainly on 

 differences and likenesses in appendages and other external 

 features. He expresses the result as regards Nebalia thus : 

 Malacostraca. 



-Nebalia. 



Phyllopoda. 



Sars (1885), on the other hand, in his Report on the 

 Schizopoda of the Challenger Expedition (1885), expressly 

 states that he cannot agree with Boas as to placing Nebalia 

 either among or near the Schizopoda. He then regarded it 

 as a Phyllopod. 



In 1885 Claus again wrote on Nebalia. After alluding 

 to Metschnikoff's paper he proceeds to give his own reasons 

 for the assertion that Nebalia is " no Phyllopod." As to 

 external features he says that there are only the following in 

 which Nebalia resembles the Phyllopods — the shell, the 

 thoracic legs, and the tail. 



The form of the shell, he justly i-emarks, is one which is by 

 no means confined to the Phyllopods. He thinks that, as in 

 the case of the Euphausia larva, it is the original mala- 

 costracan shell which has been retained. Further, he says, 

 it shows that the carapace of the Malacostraca and the shell 

 of the Entomostraca had the same starting point. The 

 thoracic limbs of Nebalia are, he continues, intermediate in 

 character between those of the Phyllopoda and those of the 

 Schizopoda. In internal structure Nebalia differs still more 

 from the Phyllopoda, and is especially like the Mysidse. 

 With regard to the abnormal number of abdominal segments. 



