246 CRUSTACEA. 



in the proboscis, a middle portion forming tlie lateral wall of the 

 proboscis, and a long, palp-like appendage provided with setae 

 and projecting freely. This latter, the outer branch of the second 

 antenna and the anterior pair of swimming appendages, are the 

 most important locomotory organs of the larva. jS'o trace could be 

 found in tlie larva of the stylet-like maxillae which are contained 

 within the adult proboscis. The two pairs of maxillipedes terminating 

 in hooks (?»/', mf") serve for adhering organs. Of the four pairs of 

 swimming limbs {p^-p^), only the anterior pair is free and movable, 

 and somewhat resembles in shape a biramose Copepodan limb. The 

 biramose rudiments of the three posterior swimming limbs are still 

 unjointed and immovable. 



During the course of metamorphosis, after several moults, the 

 basal hook-like processes of the two pairs of antennae grow stronger ; 

 the exopodite of the second antenna and tlie palp of the mandible 

 disappear, while the endopodite of the second antenna, losing its 

 terminal liook, is transformed into a simple palp. The large sucking 

 disc develops on the first maxillipede. The swimming limbs become 

 biramose and are provided with setae, thus resembling the limbs of 

 the Copepoda. In the two anterior pairs of these limbs the rudi- 

 ments of tlie inner branches, known as the flagella, appear, while 

 sexual differentiation is evident in the two posterior pairs, a char- 

 acteristic transformation of tlie protopodite taking place in the male. 



7. General Consideration regarding the Segmentation of the 

 Body and the Metamorphoses of the Malacostraca. 



In the IMalacostraca the body consists of three primary regions, 

 each of which, in all the divisions of this sub-class, contains a definite 

 number of segments. In the anterior ceplialic region, to which 

 belong five pairs of limbs (the two pairs of antennae and the three 

 pairs of jaws), there is, with few exceptions, no trace of a separation 

 into distinct segments. In the thoracic region, Avhich follows 

 posteriorly and consists of eight limb-bearing segments, while the 

 boundaries of the different segments are still more or less marked, 

 only a slight power of movement between the individual segments 

 is retained. But in the abdominal region, which consists of six 

 limb-bearing segments and a terminal portion (telson), the full 

 mobility of the separate segments is, as a rule, preserved, a fact 

 connected with the development of the posterior end of the body 

 into a swimming tail of great importance for the locomotion and the 

 steering of the body. 



