98 THE VOYAGE OF H.U.S. CHALLENGER. 



first distinction, viz., that the carinal latus is flatter and has the umbo not so far projecting 

 outwards, may arise from the difference in age, hence in size. Yet the largest specimen 

 i)i' tlic three is probably a full-grown one, as it is furnished with a complemental male at 

 each side. The difference in the number of scales of the peduncle is very considerable. 

 Whereas the number of horizontal rows is about equal to that of the full-grown specimen 

 of Station 335, the number of scales in each horizontal row is only three or four. 



The complemental males of this species are relatively large ; there are not more than 

 one on each side. One of these (attached to the left hand scutum of the largest specimen 

 of Station 3) is still in the pupa-stage. I have figured it PI. IX. fig. 7. It has all the 

 characteristics of a true pupa of a Cirriped ; however, one feels inclined to say that the 

 interior of the body is only feebly developed. The specimen figured in PI. IX. fig. 8 has been 

 taken from the right hand scutum of the full-grown Scalpellum velutinum from Station 335. 

 In this male the retrogressive metamorphosis is already far advanced. The body is 

 covered by a mantle clothed with numerous slender spines, and having two openings or 

 slits, one anteriorly, through which the prehensile antenna? are stretched forth, and the 

 other at the posterior extremity, which lets out a tuft of very delicate hairs. These hairs 

 were originally attached to the six pairs of rowing feet of the pupa, but of these feet only 

 the exuviae are still visible. Of the interior of this young male the testis (t.), with a part 

 of the vas deferens, is easily distinguished, and so are two glandular bodies, which, to judge 

 from their position, probably represent the cement glands (fig. 8, c.gl.). The comple- 

 mental male taken from the right side of the largest specimen from Station 3 is a well- 

 developed one. At least its metamorphosis is finished, and the body, enclosed by the 

 mantle with its slender spines, contains a large testis, with well-developed receptaculum 

 seminis. I have figured this male in fig. 9 of the same plate. With regard to the size of 

 the different stages, the length of the pupa-stage of fig. 7 is 1 - 3 mm. ; the more advanced 

 pupa-stage of fig. 8 measures only 1 - 1 mm., and the well-developed male of fig. 9, 1*2 mm. 

 So we see that the size during the retrogressive metamorphosis slightly diminishes. 



When we consider 1st, that it has been proved that in Scalpellum stroemii, Sars, the 

 metamorphosis of the Nauplius-larva into the Cypris takes place within the mantle cavity 

 of the mother ; 2nd, that a larva in the Cypris-stage in different species of the genus 

 Scalpellum [Scalpellum velutinum, Scalpellum eximium, &c.) has been observed at the 

 place occupied also by the complemental male ; and 3rd, that stages forming a link between 

 the larva and the male itself have been observed at the same place — we may trace the 

 life-history of these males in the following words : — 



a. Species of the genus Scalpellum (whether all of them, or only those which 



inhabit the deep sea, cannot be said with certainty) have lost the Nauplius 

 as a free swimming; larval stage. 



b. After the metamorphosis into the Cypris-stage, some of them become 



