LECTURES ON MOLLUSCA. 131 



true zoophytes, yet there is sufficient analogy between them and the 

 compound Tunicaries to entitle them to a place in the molluscan sub- 

 kingdom. They differ from even the lowest Tunicaries, in not having 

 any special circulating vessels; the fluids being generally transmitted 

 through the transparent mass of the tiny bodies. They have been 

 designated both as Polyzoa and Bryozoa; the former name being the 

 earliest, the latter the most distinctive as a class. By some authors 

 they are considered as superior Radiates, by others as degraded Mol- 

 lusks. The balance of characters seems in favor of the latter view; 

 but as they are more conveniently studied in common with the true 

 zoophytes, and are generally described in treatises concerning the 

 latter, they will not be further considered here. Those who are at 

 the sea-shore, and can examine the " sea-n>ats" and Lepralias in their 

 living state under the microscope,, will do well to examine the differ- 

 ences between them and the common Sertularian Polypes. Some of 

 the forms are peculiar to fresh waters. The test formed by their com- 

 pound zooids is often somewhat calcareous. Their remains are ex- 

 tremely abundant in the Coralline Crag; and even in the palaeozoic 

 rocks, they play an important part among the fossil keys to knowl- 

 edge. It must be borne in mind however that many of the objects 

 described loosely as Bryozoa have no relation to this class. 



Those who desire information on this interesting class of creatures 

 are referred to " Johnstone's British Zoophytes," and to the works of 

 George Busk, Esq., published by the British Museum. 



On bringing to a close this brief digest of our existing knowledge of 

 molluscous animals, any one who will take the trouble to compare the 

 nomenclature and arrangement here adopted with that of any one or 

 more of the principal treatises on the subject, will be struck with the 

 general want of harmony which prevails among the different authori- 

 ties. It will not help us out of our difficulties to ignore their exist- 

 ence. In the old days when all knowledge was supposed to be centered 

 in Lamarck, we had nothing to do but to study his system and follow 

 it. We are now turned loose on a new sea of inquiry; where every 

 voyager makes his own discoveries, which is right; and his own spec- 

 ulations, which may be correct or very erroneous. 



Our uncertainties for want of knowledge are quite sufficiently dis- 

 couraging; but for these we must be prepared. With every fresh, 

 patient, and honest observation, these will be steadily lessened, in 

 spite of the prejudice and human tempers which ought not indeed to 

 be allowed to enter into the domain of science, but alas ! are to be 

 found there as rife as in any other department where men enter on 

 each other's paths. And it ought to be an incentive to pursue this 

 branch of study that there is so much to be done; and so much, too, 

 the materials for which are easily accessible. The principal requisites 

 to insure really useful results are not indeed great talents or special 

 acquirements, which fall to the lot of but few; but what an ordinary 

 person may possess himself of, an accurate eye, patience, and honesty. 



It is well, in the present state of science., to take nothing on trust. 

 What is copied from book to book, and what is repeated^ from figure 

 to figure, may be correct; "but then, on the other hand, it may not." 

 Very few can examine all things with their own eyes; and the greatest 



