LKRN^OIDA. 141 



Tribe III. LERN^EOIDA. 



Mouth usually suctorial. Thorax not articulated, 

 or only obscurely so. Thoracic legs, when present, of 

 a more or less rudimentary structure. Body some- 

 times, as stated by Baird, " very outre in appearance."* 

 Egg-strings two, stout and of moderate length, or some- 

 times slender and greatly elongated and straight or 

 more or less twisted. Male usually very small. 



The species belonging to this tribe are all more or less 

 permanently fixed upon their hosts ; but, as stated by Baird, 

 it is in general " only the adult female of the Lernaeida9 that we 

 are in the habit of observing, and in an animal whose organs 

 of motion and perception for the most part are merely rudimen- 

 tary, and whose existence is strictly stationary, the manner of 

 life must be very simple/'t They are usually arranged under 

 the three families Lerna3idae, Chondracanthidas, and Lernseo- 

 podse, which differ, and, for the most part, are characterized 

 by the manner in which the parasites fasten themselves to the 

 fish on which they live, which also presupposes corresponding 

 differences in at least some of the other appendages, as well 

 as in the relation of the sexes. (See remarks on Lernsea in 

 the Introduction.) 



The young Lernsea leaves the egg as a free-swimming 

 nauplius, which, in general appearance, is very similar to the 

 lai'va of Cyclops. 



Family v. 



Body of the mature and fixed ovigerous female more 

 or less cylindrical, and unsegmented but roughly 

 divided into three parts a globular head with anchor- 

 like processes either simple or branched ; a narrow, 

 cylindrical, and sometimes more or less flexuous 

 neck connecting the head with the posterior part of 

 the body or genital segment ; the genital segment 

 usually more or less swollen, and straight or sig- 

 moid. Egg-strings two, slender, elongated, sometimes 

 twisted into two involved masses, or forming more or 

 less regular spirals. 



* ' British Entomostraca/ p. 307. t Op. cit., p. 318. 



