NO. 206S. NORTH AMERIGAy^ PARAStflC COPEPODS— WILSON. 581 



other coordinate differences, excellent generic characters as already 

 noted (see p. 573). In one species, Lernaeo'podma longimana, the 

 arms, as these transformed second maxillae are called, are as slender 

 as threads and fully three times the length of the entire body. On 

 the other hand some species of Clavella have no arms at all; they have 

 entirely disappeared and the attachment bulla is sessile upon the 

 ventral surface of the body. Yet even in these species we find the 

 remains of the maxillary muscles arranged in pairs on either side of 

 the sessile bulla. Between these two extremes there is almost every 

 gradation. 



The arms are usually separated to their tips, where they are united 

 to the pedicel of tlie bulla. In the genus Clavella, however, the arms 

 are fused together more or less, sometimes for their entire length. 

 When they first appear these second maxiUae are on the head and in 

 front of the maxillipeds, but during subsequent development the two 

 usually exchange places. The second maxillae then migrate onto the 

 first thorax segment and may move a long distance behind the other 

 mouth parts {Clavellisa, BrianeUa, etc.). 



The bulla is composed of the hardened secretion of the frontal 

 gland and is usually mushroom-shaped, but may be club-shaped 

 (Basanistes, Salmincola thymaUi), button-shaped (Clavellopsis sargi, 

 Brachiella in^Zas), funnel-shaped (Clavellopsis fallax), goblet-shaped 

 (Brachiella hostilis), star-shaped {Tracheliastes stellifer), or even 

 flattened out like a plate {Salmincola inermis). The way in which 

 this buUa is fastened to the host has already been described.* 



There is one thing to be added which was also noted by Kurz. 

 The viscid secretion which fastens the bulla to the skin of the host 

 acts as an irritant and causes the skin to fester and swell into a wall 

 or fold, which rises up around the bulla and finally entirely envelops 

 it. This adds greatly to the security of the attachment; in fact the 

 only way in which the parasite can be detached is by dissecting out 

 the bulla, which usually proves to be a difficult process. We should 

 also notice the pecuhar muscle bands which serve as second maxillae 

 in Naohranchia, and the unique sucking disks just outside the base of 

 the maxiUipeds (see p. 662). 



The maxillipeds.— -These are clawed appendages, similar to those 

 found in all the copepod families. They consist of a powerful basal 

 joint well supplied with strong muscles, which operate the terminal 

 claw and flex it down against the inside of the basal joint. Tlie 

 claw is usually straight or sliglitly curved, and is often reinforced 

 near the 'tip by a short spine or secondary claw. 



The inner surface of the basal joint, against which the claw shuts, 

 is also roughened and armed with various teeth, processes, spines, 

 etc., to increase the firmness of the hold. In the male the claw is 



1 Proc. U. S. Nat. Mus., vol. 39, p. 2n. 



