SEA-FISHERIES LABORATORY. 195 



mus " stage, when the maxillipedes are rudimentary. 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. 3, 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 degree 

 of maturity of the reproductive organs. In an immature 

 female (Plate II., %. 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 part 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- 



