CLAVELINA. 



CLAVICORNES. 



valves only, and to float free, with, perhaps, some voluntary impulse), 

 it arrives at the vacant hole of some small Petricola, Litkodomva, or 

 other perforating Testacean which suits it, one valve soon becomes 

 attached to the wall of the hole, and then the animal proceeds to 

 secrete the siphonic sheath or tube, to enlarge the chamber according 

 to its necessities, and to form the shelly perforated tubular plate 

 which* is to give admission to the water at the practicable part of 

 the chamber. How the excavation is carried on is also doubtful. 

 The chambers of the individuals of Clavagella auitralia, described 

 by Mr. Broderip, were formed in a siliceous grit, those of C. elongatu 

 in an Astrceopora, that of C. lata in a calcareous grit, and those of 

 C. Mclitensi* in an argillo-calcareous tufa. " If," gays the author 

 last mentioned, " the excavation be the work of a solvent secretion, 

 it must be a solvent of extensive power. The situation of the 

 glands, detected by my friend Mr. Owen, leads me to think that they 

 minister in some way to this operation ; and I do not see how the 

 anterior or greater end of the chamber can be operated on by mere 

 mechanical attrition with such parts as must have been contiguous 

 to it. It has been objected that any solvent which would act on a 

 calcareous rock would equally act on the calcareous shell of the 

 animal ; but there is perhaps more of point than of strength in this 

 objection. Without laying too much stress on that law of nature 

 by which chemical and vital forces are placed in a state of hostility, 

 and which may or may not be applicable to such a substance as 

 shell, the gland for the secretion of the supposed solvent, as well as 

 the organ for applying it, may be so placed as that the solvent shall 

 only come in contact with the inorganic or dead substance to be 

 acted on without touching the shell. Again, it has been asked, what 

 solvent would act equally on a calcareous and on a siliceous sub- 

 stance ? To this it may be answered, first, that it is not pretended 

 that the nature of the supposed solvent is known ; secondly, that in 

 siliceous grits, there is more or less calcareous matter by which the 

 mass is held together, and that the solution of the calcareous particles 

 would be followed by the disintegration of the stone ..... One 

 observation, arising from the various depths at which the recent 

 species have been found, will not, perhaps, be deemed irrelevant. C. 

 aiutralit was so near the surface at low water, that it was detected 

 by its ejection of the fluid ; C. tlongata, from the nature of the coral 

 in which it was chambered, could not have been living far beneath 

 the surface ; whereas C. lata was dredged up from a depth of 66 feet. 

 Any inferences, therefore, as to the state of submersion of a rock 

 during the life of the fossil species of Clavayella which there occur, 

 should be made with caution by the geologist." 



The geographical distribution of the genus, though now compara- 

 tively rare in cabinets, is probably wide. A sharp investigation of 

 masses of coral and of submerged perforated rocks or stones, particu- 

 larly in warm climates, is very likely to be rewarded by the discovery 

 of Clavagella. 



With regard to its place amongst the other SfoUtwca, Professor 

 Owen is of opinion that the organisation of Clavagella, like that of 

 Arpergillum described in the ' Reise von Afrik' of Dr. Riippell, is 

 modelled on the type of the Acephalous Bivalves ; and that it follows 

 most closely, in the variations from that type, the modifications which 

 have been observed in Gattrochana. The lengthened worm-like figure 

 of Atpergillum is exchanged in Clavagella, observes Professor Owen, 

 for a shorter form with greater lateral development ; and instead of 

 the small rudimentary valves, which are enchased, as it were, in the 

 calcareous sheath of Aspergillnm, we find them here largely developed, 

 and one of them always remaining at liberty, to be applied by a 

 powerful muscular apparatus to those offices which are essential to 

 the forcible expulsion of the fluid in the branchial cavity, and pro- 

 bably to assist in the excavation of its secure abode. 



fU Claragellce. 



Mr. Broderip says that no fossil species appear to have been 

 detected below the Supracretaceous group. M. Deshayes, in his tables, 

 gives two living and seven fossil (tertiary) species, and one (C. aperta, 

 Sowerby) as found both living and fossil (tertiary). He gives the 

 Mediterranean and Indian Ocean as the habitation of the living 

 animal, and Sicily (Pliocene Period of Lyell) as the locality of the 

 fossil. In his edition of Lamarck he makes the whole number (living 

 and fossil) seven, the seventh and last species being C. aperta ; but 

 he refers to Hang's ' Manuel ' for a second living species. C. coronata 

 i* found in the London Clay. In Deshayes's edition of Lamarck, the 

 species C. cchinata is followed by C. cristata ; and the editor, in a 

 note referred to from the latter, says that these two species should 

 be united, as they only differ in size and age. He also observes that 

 the free valve of C. cristata, or of C. tibialii, has been placed by 

 Lamarck among the species of Glycimerin under the name of G. mar- 

 garilacea. And here we may mention the difficulty of laying down 

 specific characters from the valves, which being, as Mr. Broderip 

 remarks, nearly, perhaps altogether, excluded from the light, colour, 

 at best but a treacherous guide, is absent entirely ; while the Hhtipe 

 of the chamber and of the valves, together with the comparative 

 roughness or smoothness of their outer surfaces, may depend upon 

 the greater or less degree of hardness of the material in which the 

 chamber is formed. 



CLAVELINA. [CLAVELIUIDJ:.] 



CLAVELINIDyE, a family of Tunicated Mollutca, including the 

 Brilish genera Ctavelina and Perophora. This family maybe regarded 

 as uniting together the Compound and Simple Ascidians. Till very 

 recently it was supposed that the animals forming this family belonged 

 to the latter. Milne-Edwards first pointed out that the animals which 

 had been described by Savigny under the genus Clavelina were not 

 always, nor even usually, separated from each other ; but that they 

 spring, as it were, from a common creeping stem, and multiply by 

 gemmation in the same manner as the Compound Ascidians. Milne- 

 Edwards also pointed out that an animal, described by Mr. Joseph 

 Jackson Lister in the 'Philosophical Transactions' for 1834, was 

 truly an Ascidian. This animal occurs in groups consisting of several 

 individuals, each having its own heart, respiration, and system of 

 nutrition, but fixed on a peduncle that branches from a common 

 creeping stem. The individual animals were connected together by a 

 circulation extending throughout the stem. They are transparent, so 

 that their structure can easily be seen through their membranous 

 covering. Milne-Edwards proposed for these animals the name of 

 Social Ascidians. 



Clavelirta, Savigny. The individuals and groups are connected by 

 creeping radieiform prolongations, the animals having elongated erect 

 more or less pedunculated bodies. The branchial and anal orifices 

 without rays ; outer tunic smooth and transparent ; thorax usually 

 marked with coloured lines. 



C, lepadiformi* (Ascidia lepadiformis, O. F. Miiller). Thorax 

 forming a third part of the length of the adult individual, and marked 

 with yellow lines ; stomach of a bright orange, placed near the middle 

 of the abdominal portion of the animal ; part of the intestines of the 

 same colour. Mr. Alder says this animal is very generally diffused 

 throughout the coasts of Great Britain. He has met with it on the 

 Devonshire, Cornish, and Northumberland coasts, and in Lamlash, 

 Rothsay, and Oban bays in Scotland. Mr. W. Thompson has found 

 it in Ireland. 



Milne-Edwards gives the following account of- the development of 

 this species : " If we examine with care the foot of a C. Icpadiformis,' 

 we see that the animal adheres to the soil by more or less numerous 

 radieiform prolongations of the tegumentary tunic ; and usually we 

 find also cylindrical filaments, which mingled with these roots and 

 formed externally by the same tissue, creep also on the surface of 

 the soil ; but are hollow, and internally furnished with a membranous 

 tube. This tube is continuous with the internal tunic of the Ascidian, 

 and the circulation which is seen in the interior of the abdomen of 

 the latter is equally continued into the appendicular canal. This 

 stalk-like body, which is closed at the extremity, is at first simple, 

 but ramifies as it elongates. When its growth is more advanced, 

 we see developing at the extremities of its branches, or even at 

 different points of its length, tubercles containing in their interior a 

 little organised mass in connection with the internal tube. These 

 tubercles elongate, elevate themselves vertically, and become clavi- 

 form ; the blood which circulates in the stem penetrates the soft and 

 pyriform central mass ; but this mass, at first peduncujated and 

 adhering to the inner tunic of the principal canal, soon separates 

 itself, and no longer participates in the circulation of the individual 

 to which it owed its origin. Nevertheless its development continues, 

 and we soon distinguish in it all the principal characteristic traits of 

 the ascidian structure ; the branchial sac becomes perfectly outlined 

 without being as yet in communication with the interior ; a curved 

 digestive tube is seen beneath the thorax. At length a buccal opening 

 is formed, and the general shape of the young animal approaches 

 more and more nearly that of the adult. Thus there is produced by 

 process of budding a new individual, linked with its parent by a radi- 

 eiform prolongation of the tegumeutary tunic, and which during the 

 first years of its life has a circulation in common with the mother 

 ascidian, but in the end enjoys an independent existence. Still how- 

 ever it may remain in connection with the individual which produced 

 it through the medium of its roots, or it may become completely 

 free by their rupture without any change of consequence in its mode 

 of life." (' Me'moires de 1'Iustitut,' vol. xviii.) 



Tnere are several other species of Clavelina, and probably many 

 more exist on our own coasts. 



Perophora. The animal discovered by Lister has been thus named 

 by Wiegmann. It is characterised by the individual animals being 

 pedunculated, suborbicular, compressed, attached by their pedicles to 

 creeping tubular processes of the common tunic, through which the 

 blood circulates. Thorax not liueated by granular bands. 



P. Lifterl is the only species at present known. It is a minute 

 creature, and occurs not unfrequently on the south coasts of England 

 and in the Irish Sea. It lives attached to sea-weeds, and is beautifully 

 transparent. It looks to the naked eye like little specks of jelly dotted 

 with orange and brown, and linked by a silvery winding thread. Mr. 

 Lister's paper describing this animal is entitled, ' On the Structure 

 and Functions of Tubular and Cellular Polypi, and of Ascidiac.' It 

 is an admirable paper, and was one of the first-fruits of those labours 

 on the improvement of the microscope for which the world is indebted 

 to Mr. Lister. 



CLAVICO'RNES, a name given by Latreille to a sub-section of 

 Coleopterous Insects of the section Pentamtra. 



The insects of this sub-section almost lwys have the antenna; 



