Feb. 1, 1S66.] 



SCIENCE-GOSSIP. 



31 



appearance of being slightly raised in relief, on their 

 connecting skin or integument. Eorbes enumerates 

 six species of Botryllus, besides Botryllidse and 

 similar objects. The size of each individual is about 

 one-twelfth of an inch. Botryllus represents the 

 ' true compound Ascidians." 





Fig'. 23. Butrylltis polycycla.s. 



Next let us take up out of the dredge some of 

 these " associated Ascidians," queer misshapen 

 masses. Their slimy, tough, leathery, and yet soft, 

 horn-like substance is not pleasing to the touch ; 

 indeed, at first it is rather repulsive, and reminds us 

 of the " Deadman's bands " {Alcyonium digitatum), so 

 disgusting an object until we have seen the beau- 

 tiful polypes which emanate like flowers from the 

 warts spread over its surface. Our tunicated 

 Ascidians exhibit no such polypes. 



It is said that most of the tunicata undergo a sort 

 of tadpole state on first emerging from the egg, 

 swim about freely in the early stages of their ex- 

 istence, and pass through curious transformations, 

 before they become fixed on the ground, or rocks, or 

 alga?, as found in their fully developed condition. 

 Let us select this dark orange-coloured lump, or 

 mass of lumps : it is probably Cynthia rustica 

 (fig. 21). There are no polypes or whorls of tenta- 

 cles on then - rough, wasted, wrinkled surface ; 

 but iuside each of the agglomerated coriaceous 

 lumps, which are really the tunica-, is an animal— a 

 true Ascidian ; and if we place the mass iu sea-water 

 we shall presently see two snouts or tubes of a bright 

 red colour pushed out from each conelike projection; 

 these have a square sort of opening, and the one 

 takes in and the other ejects the fluids which sup- 

 port the life of the animal. These fluids are some- 

 times ejected with such force, that Mr. Gosse has 

 called these creatures " squirters " ; the tubes are 

 called syphons. There are about thirteen species of 

 Cynthia recorded. The animals resemble a good 

 deal in some respects, and differ in others from, those 

 of the Pholas and other allied families of the true 

 Mollusca ; but instead of shells they are invested in 

 these tough coriaceous tunics, or jackets, and are hence 



named Tunicata, of which about seventy-four species 

 are described by naturalists. M. Milne-Edwards 

 has written very elaborately on the Ascidia ; but the 

 merit of first detecting their real nature belongs pro- 

 bably to Savigny ; though they seem to have excited 

 the attention of Aristotle, who gives a most graphic 

 description of them when he says : " They are the 

 only kind of mollusca whose whole body is enclosed 

 in the shell, and that shell of a substance between 

 true shell aud leather ; it may be cut like dry 

 leather. If we open them we find a nervous mem- 

 brane lining this leathery case, and fixed to it at 

 two points, corresponding to the two separate open- 

 ings, the one to take in, the other to eject the water." 

 He then makes further remarks on their anatomy, 

 which convinced him of their truly animal nature, 

 although on the first mere external survey, the 

 inert and sponge-like forms rooted to the ground 

 seemed to indicate a vegetable nature. Like most 

 philosophic naturalists, the question of the distinc- 

 tion between the animal and vegetable kingdoms 

 was one of great attraction for the all-observing 

 Aristotle, and this great father of natural history 

 examined the Ascidia and many other creatures in 



- 3fiW 



Fig. 2-1. Cynthia, and its Tadpole. 



the hopes of gaining definite information respecting 

 such distinction. This line of demarcation is 

 eagerly sought after to the present day, but, as yet, 

 the subtlest chemistry, the most unwearied micro- 

 scopic searchings, have failed to settle the question. 

 May it not be that the mingling and melting of one 

 nature into the other are too gradual and impercep- 

 tible for human ken ? 



It is worthy of remark that, so lately as 1845, the 

 Ascidians have again played a part in that much- 

 vexed question, and been obliged to submit to new 

 cross-examination, and with very unexpected results, 

 for they have shown in the composition of their 

 tissues an unlooked-for relation with vegetable 

 structure. 



Dr. Schmidt discovered in the tunic of an 

 Ascidian mollusk a substance identical with cellu- 

 lose. This statement was confirmed and extended 

 by the inquiries of Professors Lowig and Kolliker, 

 who found cellulose undoubtedly present in con- 



