SOME OTHER CRUSTACEA. 211 



pink, especially about the antennae. You will notice also 

 the large, very movable eyes, usually outspread laterally, 

 but capable of much freedom of movement. Also the 

 curious bend in the middle of the body, which gives rise 

 to the name flexuosa, and has at times almost the look of a 

 deformity. The larger specimens will be found to be over 

 an inch in length, but many are much smaller. With the 

 lens there is no difficulty in making out that there are eight 

 pairs of legs, very similar to one another, and that all of 

 them consist of two branches. It is on account of this and 

 of some other characters that Mi/sis is included in the order 

 Schizopoda, or "split-footed," as contrasted with the Deca- 

 poda, or Crustacea with ten legs, already described. The 

 Schizopods are even more purely swimmers than the Natantia 

 among Decapods; they have no walking legs, strictly speaking, 

 and their eight pairs of thoracic legs resemble one another 

 very closely. 



The My sis described above is by far the commonest 

 member of its order on the shore, for the great majority 

 of its relatives live in the open sea, but there are a few 

 other nearly related forms which occur more sparingly along 

 with Mysis flexuosa^ or are occasionally found far out at 

 exceptionally low tides. All these belong to the family 

 MysidaB, and resemble one another so closely that their 

 discrimination requires some care. Those who are fond of 

 species work will find Mysidae peculiarly fascinating, while 

 others are recommended to rest content with Mysis flexuosa. 

 We shall describe one or two representative species only. 



To begin with the large Mysis flexuosa. We have already 

 seen that it belongs to the order Schizopoda; it further 

 belongs to the family Mysidae because of the following 

 characters. Its eight pairs of thoracic limbs are similar 

 but not identical, for the first two have a masticatory 

 process at their base, and the first has also a flat vibratile 

 appendage. Some of the posterior thoracic limbs bear 

 somewhat similar appendages, which here, however, are 

 apposed so as to form the brood pouch in the female. Gills 

 are entirely absent. There is much difference between the 

 sexes, especially as regards the abdominal appendages, for 

 these, except the last pair, are well developed in the male 

 and rudimentary in the female. The inner branches of the 



