1919 Fasten; on Salmincola 161 



now sets in (Fig. 27), and soon the organism begins to lose its segmenta- 

 tion, while at the same time the feathered setae of the abdomen and swim- 

 ming feet disappear. The swimming feet themselves become stub-like 

 (Fig. 27, f and f") and are ultimately absorbed entirely. The abdomen 

 and the rest of the body round out and become more bag-like in appear- 

 ance. The mouth appendages also change. The mouth tube grows more 

 prominent (Fig. 27, m.t) ; the first and second antennae (Fig. 27, a' and a") 

 become smaller and more stump-like in appearance. Perhaps the most in- 

 teresting modifications take place in the second maxillae and maxillipeds. 

 The former (Fig. 27, mx"), which are now attached by their claws to the 

 foot of the attachment filament, lose their segmentation and begin to 

 thicken considerably ; also their terminal claws become smaller in size. 

 The maxillipeds (Fig. 27, mxp) likewise thicken, grow somewhat in size 

 and their terminal claws undergo modification. 



Internally the digestive system (Fig. 27, d) has grown in size, specially 

 the stomach. The glands may be quite easily traced. The sex-organs be- 

 gin to shape themselves. The eye (Fig. 27, e) undergoes degeneration. 



The changes just described occur during the first five or six days 

 after attachment. From now on the copepod begins its active growth and 

 development toward sexual maturity. This is completed in about another 

 week and a half during which the mouth tube becomes very active, suck- 

 ing abundant nourishment from the host. The body elongates and grows 

 vigorously (Figs. 27 to 29, and 31), while the appendages, glands, diges- 

 tive system, sex organs and other structures develop still more completely. 

 Males and females may be found hanging side by side on the gills of the 

 fish ; however, the former are pigmies as compared with the latter. 



Perhaps the most interesting changes which occur during this period 

 are those which take place in the second maxillae and the maxillipeds. 

 The second maxillae of both males and females are short, stout structures 

 with their terminal claws driven into the foot of the attachment tube (see 

 Figs. 28 to 31, mx" and t). A careful examination of the region of at- 

 tachment between the maxillae and the foot of the attachment filament 

 reveals the fact that this attachment is not as yet permanent, and that 

 the second maxillae may withdraw their claws in order to shift their posi- 

 tion. This is specially well shown in Fig. 30, which is an enlarged drawing 

 of the attached portions of the second maxillae shown in Figure 28. When 

 figure 30 is examined it is seen that the foot (ft) has been pierced a num- 

 ber of times at the places marked x, by the claws of the second maxillae 

 (mx"). 



The maxillipeds (Figs. 28, 29 and 31, mxp; 32 and 33) remain 

 jointed but transform completely. They become more conspicuous; their 

 thickness and length increase, particularly that of the terminal segment. 



