ASCIDIA.- 



-MOLLUSCA.- 



- BoTrtYLLlD.E. 



383 



is extiemcly accurate. On the coasts of the Mediter- 

 ranean and in China (where species of AsoidicE occur), 

 several of them are esteemed as articles of food. Van 

 Beneden informs us that at Cette Ascidias are taken 

 regularly to market, and that a particular species 

 (Cynthia mkrocosmus), "although so repulsive exter- 

 nally, furnishes a very delicate morsel, much sought 

 after by some." 



Genus Ascidia or Sea Squirt. — This genus is 

 known by its sessile body beingcovered with a coriaceous 

 or gelatinous tunic; the branchial orifice being eight- 

 lobed, and furnished inside with a circle of simple ten- 

 tacular filaments ; the anal orifice is six-lobcd, and the 

 branchial sac is not plaited. The species vary in 

 length from one to five or six inches, and range from 

 low water to twenty fathoms. In some of the Ascidis 

 the external tunic is pale and seraitransparent, and the 

 inner coat is orange or crimson, or sometimes marbled 

 with orange and white. Most of them, however, as 

 Sir John Dalyell says, " are coarse, unsightly, deformed- 

 looking animals, utterly void of that external symmetry 

 and beauty rendering many of the tenants of the waters 

 so interesting. Nor is it in this only that they should 

 fail to attract the spectator's notice. They testify 

 neither instinct, action, nor motion, nor even the symp- 

 toms of life, farther than slight enlargement and reduc- 

 tion of size, together with contraction and expansion 

 of the two tubular orifices of the body. No sensible 

 attraction follows abstinence or repletion ; the external 

 form undergoes scarcely any modification from health 

 or disease ; even the lapse of time, that universal con- 

 sumer, seems hardly to make any impression on the 

 shapeless mass, which is rooted immovably from the 

 first moment on the same spot to vegetate, live, or 

 die." 



GicKUS Cynthia. — This genus is sessile as well as 

 Ascidia, and its test or tunic is coriaceous; both bran- 

 chial and anal orifices are four-lobed, and the branchial 

 sac is plaited longitudinally aud surmounted by a circle 

 of tentacular filaments. About fourteen species are 

 described as inhabiting the coasts of Great Britain, and 

 they are foimd ranging from low water to thirty fathoms. 

 Individuals are often seen unattached as well as fixed, 

 though, as Mr. Rupert Jones observes, these animals 

 " cannot be said to have an entirely free existence, their 

 tests being usually more or less imbedded in sand or 

 mud, and frequently h-eld to their anchorage by the 

 agglutination of the surrounding sand-grains to their 

 outer surface. But from such a position they are easily 

 disturbed." The species of Cynthia are also frcipiently 

 found associated in groups of numerous individuals, 

 forming large bunches in consequence of the interlacing 

 of their root-fibres. The genus is represented by two 

 species, C. monuis and C Canojyios (Plate 9, figs. 

 7 and 9). 



Genus Boltenia.— This genus instead of being ses- 

 sile, as in the two preceding genera, has its coriaceous 

 body fixed by a pedimcle to stones, often in deep water. 

 Sometimes young Boltenise fix themselves on to the 

 stem of their parent. In tliis genus the orifices are 

 lateral, and both of them are cleft into four lobes or 

 rays; the branchial sac is longitudinally plaited and 

 surmounted by a circle of compound tentacles. 



Two other genera belong to this family, MoUjnIa 

 and Chehjsoma — the one (Molgula) having a mem- 

 braneous tunic or test, but usually invested with sand 

 or other extraneous matters; the other having its 

 coriaceous test resembling the carajiace of a tortoise. 



Family II.— CLAVELLINID.a; {Social Ascidiwis). 



The " Social Ascidians " are very small animals found 

 on stones, shells, and sea-weed, adhering by numerous 

 root-like projections of their outer tunic. As their 

 name indicates, these animals occur in groups of several 

 individuals, each liaving its own heart, respiration, and 

 system of nutrition, but fixed on peduncles or stalks 

 that branch from a common stem, through which the 

 blood circulates in o]ipo.site directions. They are such 

 transparent and colourless animals, that their internal 

 structure can be seen without dissecting them. Repro- 

 duction takes place in these Social Ascidians by gem- 

 mation or by the process of budding, as well as by 

 eggs. The new individuals so formed may continue 

 united to the parent, or may bccoro'" oompletuly free 

 liy the rupture of the connecting tube. 



Genus Clavei.una. — In this genus the individuals 

 composing the compound body are connected by creep- 

 ing tubular prolongations of tlieir common tunic. They 

 are elongate, erect, more or less pedunculated; the 

 outer tunic is smooth and transparent, and the thoracic 

 portion of llie body is usually marked with colouied 

 lines. The branchial and anal orifices are both sinjple, 

 without lobes or rays. The specic!s which have been 

 observed are found in the northern seas and in the 

 Jlediterranean. This genus is represented by C. horcalis 

 in Plate 9, figs. 5 and 6. 



Genus Perophora. — This genus ditTers from the 

 preceding in the individuals being suborbicular and 

 comjiressed, and the thoracic portion of the body being 

 destitute of coloured lines. There is only one species 

 known. It is beautifully transparent, according to 

 Professor Forbes, who has dredged it adhering to sea- 

 weed on the coast of Anglcsea, and appears like little 

 specks of jelly dotted with orange and brown. When 

 dried, these bodies appear like the minute ova of some 

 mollusk. 



Family III.— BOTRYLLID.^^ {Compound 

 Ascidians). 



The Botryllidce are compound animals, and fixed. 

 The animals are associated with each other, their tests 

 being fused together so as to form a common mass in 

 which they are imbedded in one or more groups. Each 

 individual, however, has a distinct branchial and anid 

 orifice, and they are not connected with one another by 

 any internal union, "If, when walking on the sea- 

 shore about low water mark, we turn over large stones, 

 or look under projecting eaves of rock, we are almost 

 sure to see translucent jelly-like masses of various hues 

 of orange, purple, yellow, blue, grey, and green, some- 

 times nearU' uniform in tint, sometimes beautifully 

 variegated, and very frequently pencilled as if with 

 stars of gorgeous device ; now encrusting the surface 

 of the rock, now depending from it in icicle-like pro- 



