CRUSTACEA MALACOSTRACA. IV. 75 



Some further points may be mentioned. The musculature in legs may sometimes be of importance 

 for the study of homology of joints, but the disappearance of musculature from a joint cannot as a rule be 

 used in morphological interpretation, because muscles are not found when a joint shall not be moved; by 

 fusion of two joints in an appendage the movement between them ceases, and when a joint is much reduced, 

 its chitinized part proportionately small, muscles to its movement are frequently not found. From detailed 

 study of the musculature in the head of various families of Diptera I have learnt, that a moderately well 

 developed morphological element is in one family completely without musculature, while in other families 

 it has an active, not only a passive function, is consequently larger and equipped with muscles. The chiti- 

 nized tubes or plates of an appendage are the most important elements in morphological 

 investigation; the musculature is secondary. 



As the order Nebaliacea generally and with good reason is considered as the lowest type among 

 the Malacostraca, one may expect that the appendages show some primitive features rather well preserved. 

 Consequently my old "theory", that in the antennae, mouth-parts and legs of Crustacea the sympod consists 

 originally of three joints, should find some support in this order, and we shall see how far it can be realized. 

 But before entering the topic a few remarks on the performance of such investigation may be made. In order 

 to study the chitinized elements of appendages, especially of mouth-parts of Crustacea (or Arthropoda), 

 it is frequently necessary to have the musculature partly or totally removed. It can be made in different 

 ways, but it is sometimes necessary to put the object in a convenient solution of caustic potash, then to 

 remove the dissolved contents by cautious handling in water or glycerine, examine the animal or the ap- 

 pendage first under the simple microscope, because it is then possible by the aid of two knifes as broad as 

 a well-sized needle to discover the limits between the membranous parts and the more firmly chitinized 

 elements ; when laid under the compound microscope the cover-glass must be hindered by a minute wooden 

 wedge from pressing the appendage. 



The order Nebaliacea comprises 4 valid genera; but of Nebaliella Thiele and Nebaliopsis G. O. S. 

 I have only a single young specimen of each genus, and the following study is in the main made on Nebalia 

 bipes from Greenland. As Nebaliella exhibits two primitive features in the antennae, Thiele's representation 

 and an observation of my own are referred to. 



The Antennulce (fig. 10 a) are described by Sars and Thiele as having the peduncle 4-jointed, which 

 is correct, but what they name first joint consists of two different parts. The large proximal part of this 

 so-called joint must be interpreted as a protuding portion of the head (h) ; it is on the outer side marked 

 off from the skeleton behind it by a fine curved line, which neither in Nebalia nor in Nebaliella shows the 

 slightest degree of movability, when one attempts to move it by two minute knifes; furthermore the right 

 protruding portion is united on the lower side with the left portion without any suture, and the whole undi- 

 vided lower wall is well chitinized; at the distal end of this solid part is seen a narrow transverse band (1), 

 which is firmly chitinized and very movable, in reality the first joint of the antennula. The 3 following joints 

 of the peduncle are well known. 



The Antenna- (fig. 10 a) are described by authors as having the peduncle 3-jointed in Nebalia and 

 Paranebalia, 4-jointed in the two other genera; it has been seen by Sars and Thiele that in Nebalia the third 



