8 



Mius " stag-e, when the maxillipedes are nidiinentary. Pro- 

 bably in the adult it acts as a first aid in securing the 

 animal to its host. Passing backwards from this sucker, 

 but distinctly over it, there is a transparent rod {c, fig. 1, 

 Plate I.: fig. ■], Plate III.), lying inside a triangular 

 blood space, which terminates in a gland (c g, fig. 3, Plate 

 III.). The gland is probably the organ that secretes the 

 substance for the filament in the " chalimus " stage and 

 the rod the remains of the filament. The filament and 

 duct are in actual contact during the early part of the 

 parasite's life (Plate I., figs 4 to 6, c). The eyes, two in 

 number, are situated in the middle of the cephalo-thorax. 

 The frontal and lateral margins are surrounded by a trans- 

 parent membrane with faint transverse lines. This 

 membrane is simply an extension of the chitinous exo- 

 skeleton which covers the whole animal. It has 

 frequently a serrated edge caused by tearing. 



The second part of the body is very small, and repre- 

 sents the fourth thoracic segment of the pelagic Copepoda. 

 The fourth feet are attached to the external margins of 

 this segment. 



The third part of the body known as the " genital 

 segment," is of variable shape, according to the degiee 

 of maturity of the reproductive organs. In an immature 

 female (Plate II., fig. 6), it is usually very little larger 

 than the fourth part, whilst in a mature one it is nearly 

 as large as the cephalo-thorax. The genital segment of a 

 mature female is somewhat quadrangular in outline, 

 slightly wider posteriorly than in front. The same 

 segment in a mature male (Plate I., fig. 2) is oval in shape 

 and about one-third wider than the fourth part. 



The fourth j^art of the body is short and narrow, being 

 only one-fourth of the width of the female genital seg- 

 ment, and corresponds to the abdomen of the pelagic Cope- 



