1919 Fasten; on Salmincola 155 



of a very broad basal portion, a somewhat more slender middle part, and 

 a third joint that carries a pronounced curved claw. 



The mouth tube (Fig, 2; Fig. 23, m.t) is placed between the antennae, 

 and is well developed in the free-swimming larva. It consists of an upper 

 (Fig. 22, u. 1.) and a lower lip (Fig. 22, 1. 1.), which are distinct and 

 separate structures joining near their bases. This distinctness of the lips 

 can be observed to best advantage when a section through the mouth re- 

 gion (Fig. 15) is studied. In the living larva the mouth tube is constantly 

 moving above and below the anterior margin of the cephalon. 



Beneath the mouth tube are the mandibles (Fig. 3; Fig. 22, mnd) 

 and the first maxillae (Fig. 6; Fig. 22, mx'). Both of these are minute struc- 

 tures, uniramous and one-jointed. The mandibles (Fig. 3) are tipped with 

 two spines, of which the inner is about twice as long as the outer. The 

 first maxillae (Fig. 6) are chela-like in character. 



The second maxillae (Fig. 7; Figs. 22 and 23, mx") are large, pow- 

 erful and distinctly three-jointed. The last of these joints bears a prom- 

 inently hooked claw of great strength. 



The maxillipeds (Fig. 8; Fig. 23, mxp) lie directly below the second 

 maxillae and like these are uniramous, large, and very powerful. The 

 maxillipeds possess three joints and terminate in a strong slightly curved 

 claw. 



The swimming feet are biramous structures (Figs. 9 and 10) possess- 

 ing broad, laminated exopods and endopods. In a previous publication 

 (Fasten, 1913, p. 38) the author made the following statement regarding 

 the swimming feet: "The thorax has two segments and these bear the 

 two biramous swimming feet, which end in broad laminated bases — the 

 respective exopods and endopods. Each exopod termintes in four long 

 feathery setae, whereas the endopods contain seven of these structures." 

 Since making the foregoing assertions, the writer has carefully re-exam- 

 ined his material, and while the above facts hold true for the first pair 

 of swimming feet (Fig. 9) they are only partially true for the second 

 pair (Fig. 10), whose exopods have four feathery setae and whose endo- 

 pods have six. 



B. Internal anatomy 



The internal anatomy has been worked out from the study of a great 

 number of whole mounts of the organism, and particularly from the study 

 of large numbers of sections of the first copepodid larvae made in trans- 

 verse, sagittal, frontal and angular planes. 



a. The eye of Salmincola edtcardsn (Olsson) Wilson is fully de- 

 veloped in the free-swimming larval stage. Wilson (1911 and 1915), 

 after studying the eye of Achtheres ambloplitis Kellicott, one of the Ler- 



