12 THE VOYAGE OF H.M.S. CHALLENGER. 



what more distinct. Perhaps the indistinctly striated condition of the fibres is the 

 consequence of their being nearly functionless and rudimentary. 1 



From their position close to the body-wall one feels inclined to compare these muscles 



together with the outer wall of the body with the " Hautmuskelsehlauch " of worms, as 



the Germans call it, The muscular fibres form a single layer only ; they have an irregular 



oblique direction, which in some parts approaches to a transverse, in other parts to a 



longitudinal, position ; their course is imperfectly parallel. Their structure is very simple, 



and can be best studied in Canada balsam preparations; when seen in oil of cloves 



their transverse st nation is so indistinct as to be hardly visible. It is from such a 



preparation that the fig. G, PI. IV. has been made. When making a preparation of them by 



means of needles they present themselves like flat bundles of delicate fibrilhe, each bundle 



having a- breadth of about 0"01 mm.; they sometimes show a clear wall as a kind of sheath, 



and are furnished with nuclei at intervals; the latter are elongate, and, as appears on a 



transverse section of the muscle, cylindrical ; they have a length of about 0'02 mm. and 



a transverse diameter of about - 005. In a transverse section of the wall of the body, 



as in all the figures of PL III., the nuclei of the matrix are seen between the chitinous 



outer wall and the transverse sections of the muscles. In these sections the latter show 



a very curious structure (PI. IV. fig. 5) ; whereas that side of the muscle-fibre which is 



directed towards the anterior of the animal is smooth and arched, and shows the sheath 



in the form of a distinct margin ; that side of the same fibre which is directed towards 



the exterior is deeply toothed ; here the fibrillar which compose the fibre seem to part in 



different ways. As I could observe this phenomenon only in very thin sections, there can 



be no doubt that this structure does not agree with the natural condition of the fibre. 



The nucleus of the muscle-fibre is sometimes placed near the outer wall, sometimes almost 



in the centre of the fibre. As to the development of the muscle-fibre, when comparing 



it with the condition of the muscular fibre in the Cypris-larva, we may suppose that the 



oval contractile cells which compose the larval fibre grow out into long fibres, the pointed 



extremities of which are no longer placed in a longitudinal row, but have been pushed 



alone: each other. 



TJie connective tissue is composed of fibres, but also of extremely delicate and finely 

 granulated membranous plates which form the partitions between the large meshes. Its 

 nuclei are round and flat, and have a diameter of 0-008 mm. The fibres are more robust 

 where they form the wall of the cavity in which the thorax is situated; we find also 

 stronger fibres where they run in a straight direction from the organs to the wall of the 

 little animal. 



I have not observed a true body-cavity in these little males, and before 1 had 

 studied the bodies of other Cirripedia by means of transverse sections, I was much 



1 Leydig (Zum femeren Ban deri Arthropoden, Arch.fiir A,,.:', wnd Physiol., 1855, p. 394) says that the muscle- 

 fibres of young individuals of Coccus hesperidum are di itinctly transversely siriate.l, tho-e ,,f full-grown individuals which 

 almost lost the function of locomotion are totally rudimentary (and smooth ?). 



