408 POLYZOA 



the cilia lining the under surface of the endocyst. Beyond this, 

 there is nothing that can be called a circulation, and there are no 

 distinct circulating organs of any kind. The nervous system in 

 all the polyzoa consists of a single small ganglion (Fig. 2d) placed 

 upon one side of the oesophagus, between it and the anal aperture, 

 and is apparently really of a double nature. Besides the single 

 ganglion which belongs to each polypide, there is, in some of the 

 Polyzoa, according to very high authorities, a "colonial nervous 

 system," which unites together the various zooids forming the 

 colony, and brings them in relation one with another. Some high 

 authorities deny that the so-called " colonial nervous system " is 

 really a nervous nature at all. 



So far as is known, the Polyzoa are hermaphrodite, each poly- 

 pide containing an ovary and testis (Fig. 2,/'/). There are no 

 efferent ducts, and the reproductive organs and the products of 

 generation — /.<?., the spermatozoa and ova — are discharged into the 

 perigastric space, where fecundation takes place, and the impreg- 

 nated ova escape by special openings in the body-wall by 

 dehiscence of the cell, or in some manner as yet not thoroughly 

 understood. Continuous gemmation occurs in all the Polyzoa, 

 the fresh zooids thus produced remaining attached to the organism 

 from which they were budded forth, and thus giving rise to a 

 compound growth. I am indebted to Professor Alleyne Nichol- 

 son's admirable work for the morphological and physiological 

 account, as well as for the figures Nos. i, 2, and 3. 



The microscope has in this, as in so many other instances, 

 been the chief factor in the elimination of the life-history and 

 physiology to which I have directed your attention. As microsco- 

 pists, I feel sure you will take a lively interest therein. I have 

 been desirous to study the life-history and development of these 

 minute organisms, and as far as possible to note the changes in 

 their structure and appearance during the countless ages which 

 have elapsed since they first inhabited the seas and some other 

 waters of this globe of ours. 



Those small organisms — the fossil Polyzoa belonging to the 

 Primary, Tertiary, and Recent geological periods — have left abun- 

 dant evidence of their continued existence from Primary times in 

 the various strata. We find remains of them in the Lower 



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