458 TERMINOLOGY OF TUNICATA : 



of our nomenclature, as a medley of" barbarous and jaw- 

 breaking words; but were these as harsh and unspeakable as 

 were the surnames of the Scotch to the musical ear of Mil- 

 ton, yet the fact would not do away with the necessity of 

 your learning them. The artisan would smile at the sim- 

 plicity of the man who should require him to explain the 

 parts of the intricate machinery he guides, without the vise 

 of the terms of his craft.'* It is needless, however, to dwell 

 upon such an obvious point; and so, with the humility of an 

 apt scholar, you will now follow me through some di-y details, 

 into which it may be impossible, perhaps, to enter without 

 the determination to turn them into future profits 



I. TERMINOLOGY OF THE TUNICATA. 



The terms used in describing the constituents of this class 

 are few. The Tunicata are — simple (Fig. 82), when every 

 individual is complete in itself; social, 

 when several individuals are connected 

 together by a creeping tube ; and com- 

 pound, when many are organically com- 

 bined and associated together to form a 

 common mass. 



The external covering of the single in- 

 dividual, and of the compound mass, is 

 called its mantle or tunic; and the inner 

 coat which immediately invests the vis- 

 cera is the branchial sac. There are two 

 corresj)onding apertures in the mantle 

 and sac; one, distinguished in general by 

 being more elevated than the other, is the branchial (Fig. 

 82, a), and the other {h) is the aiial orifice or vent. The 



* " It is frequent, even with some who pretend to be naturahsts, to vihfy 

 the fundamental parts of natural history ; who view the particular species 

 and bodies in nature ; their systematic arrangement ; their correct denomi- 

 nation ; and tlie description of tlieir parts and properties ; as a study too 

 minute, frivolous, and beneath their notice ; whose large views are only 

 diiected to what they call the volume of nature, and the great lines in natu- 

 ral history. But I know of no great lines in natural history that are not 

 composed of small ones ; nor have I ever had occasion to admire any man's 

 knowledge concerning a great line, that was ignorant of its component 

 parts. 



" As for their volume of nature — like other volumes, it consists of pages ; 

 and those pages, of lines, words, and letters. But without an acquaintance 

 with these, we have no more riglit to pretend to understand this boasted 

 volume, than we would to have to understand a book, whose letters, words, 

 lines, and pages, we have never perused." — Dr. Walker, Eisai/s on Nat. 

 History, p. 334. 



