10 THE VOYAGE OE II. .M.S. CHALLENGER. 



b. ANATOMY OF THE MALE OF Sco.ljx II u in riijium. 



I will now proceed to give an anatomical description of the complemental male of 

 Scalpellum regium (Wyv. Thorns. ), Hook. I choose this species because it is represented 

 by numerous specimens, and also because it is one of the largest species in the Challenger 



Collection. 



Form and dimensions. — The complemental male of Scalpellum regivm lias an 

 elongated oval shape. Its length varies from 1*6 to 2 - 4 mm., its breadth is U'G3 to 

 071 mm. The difference in length corresponds to differences in some of the internal 

 parts, especially of the testis. Whether it is occasioned by the growth of this organ I 

 cannot say. The third dimension, the thickness, is nearly equal to the breadth. We 

 may call the extremities of the longer axis the poles of the body, and I propose to call 

 one tlie peduncular, the other the capitular pole (PI. I. fig. l). 



The Antenna. — The only appendages visible externally are the small antennae, 

 situated close to the extremity of the body corresponding to the peduncle of other 

 Cirripedia ; they are seated at a little distance from the extremity, on that side of the 

 body which represents the ventral surface. They have two segments; one cylindrical, 

 and about twice as long as the other, which is flat and triangular. What Darwin calls 

 the third and ultimate segment of the antennae is very distinct in the case of this little 

 creature (PI. I. fig. 3). It is articulated to the upper surface of the disk, and directed 

 rectangularly outwards. Whereas the main segments of the antennae are not furnished 

 with spines, this latter segment bears five spines at the end, and three very slender ones 

 at a notch a little beneath the extremity of this segment. 



With the aid of these antennae the little creatures are attached to the inner surface 

 of the scutum of the hermaphrodite or female. The triangular terminal segment of the 

 antennae, in all the cases 1 observed, surrounded the extremity of a transparent mass, which 

 I think can safely be considered as the product of the cement-glands which are in relation 

 with I he antennae. It is by means of this cement that the attachment of the triangular 

 disk takes place. In the case of Sculpclhnn regium the males are attached a little above 

 the adductor muscle, and, as a rule, three of them are implanted so closely together as to 

 touch each other. What I think very peculiar is, that in three different cases observed 

 by me, two of the three males attached to the scutum were much further developed than 

 the third ; the first contained a fully developed testis and a well-filled vesicula seminalis, 



the third was still in the conditi f a Cypris-larva (PI. IF. fig. 3), probably only lately 



attached to undergo its final metamorphosis. 



The wall of the body is a chitinous skin, which is comparatively thin and delicate; 

 when a transverse section of the body is made, the chitinogenous epithelium beneath the 



