1744 THE VOYAGE OF H.M.S. CHALLENGER. 



auci compose the spiny surface of the peculiar "fork-thicket;" whilst in the Coelo- 

 graphida they become connected by frequent anastomoses and form the outer " lattice- 

 mantle." The styles, however, are much longer, projecting over the surface of the 

 thicket or the mantle, and are not dichotomously branched, but verticillate, or armed 

 with cruciate or alternately cruciate pairs of branches ; the larger branches of the styles 

 may be again dichotomously branched, like the brushes ; whilst the free prominent parts 

 of the styles are always verticillate or cruciate-pinnate. The brushes are identical with 

 the hollow tul.)es of the Ccelodendrida, whilst the styles are peculiar forms of apophyses, 

 wanting in the latter. 



The minimum number of hollow tubes which arise from each valve is three, and these 

 are probably homologous with the three primary tubes of the Ccelodendrida. Two of 

 these are paired (right and left), whilst the third is odd and lies in the sagittal plane ; 

 they have the same position as in the tripodal Nassellaeia, and may therefore bear the 

 same names, the two paired anterior or pectoral tubes being divergent forwards, the odd 

 or caudal tube being directed backwards (so in the Ccelotholida, PI. 121). The odd 

 caudal tube (proljably identical with the odd tube of the Ccelodendrida) is always a 

 brush, dichotomously branched, and never prolonged into a free style. The two paired 

 frontal or pectoral tubes, however, are usually prolonged into two long verticillate styles. 

 The basal origin also of these three primary tubes is different. The two pectoral or 

 anterior paired tubes always arise from the galea itself, whilst the posterior odd or 

 caudal tube usually arises behind the galea from the valve (PL 127, figs. 4-8, g 6). 



Since these three primary tubes, the odd caudal and the paired pectoral, are probably 

 homologous in all Coelographida and Ccelodendrida, they have a great morphological 

 importance, similar to the three primary feet of the Nassellaria. All other tubes arising 

 from the valves must be regarded as secondary apophyses, since they are not constant 

 in all members of the two families, but present only in some of them. All the Ccelotho- 

 lida observed (a small number of species only) possess no secondary tubes, but only the 

 three primary ; whilst all Coeloplegmida possess one or more secondary tubes, and one of 

 these is constant, viz., the odd nasal style, directed towards the mouth, and arising as 

 the foremost from the apex of the galea (PL 127, figs. 4-8, g \)- 



The maximum number of tubes observed, which arise from each valve in the Coloepleg- 

 mida, is eleven ; five of these are odd and placed in the sagittal plane of the body, viz. : — 

 (A) the primary caudal tube (PL 127, figs. 4-8, g 6); (B) an odd procaudal tube, arising 

 between the caudal and the sagittal tube ; (C) the sagittal tube, placed either in the 

 sagittal axis of the body or near it (often prolonged into a sagittal style, PL 128, 

 fig. 1); (D) an odd postnasal tube, arising between the sagittal and the nasal tube; (E) 

 the odd nasal tube, constant in all Coeloplegmida, and connected at its base by the odd 

 frenulum wth the rhinocanna (PL 127, figs. 4-8, g I). All other tubes occurring in 

 the Coeloplegmida are paired, and symmetrically arranged on both sides of the sagittal 



