MOVEMENTS OF VIBRACULA IN CABEREA BORYl. 



vidually but in companies, obedient to a common impulse ; 

 and in such a case it seems impossible to doubt that there 

 must be some special nervous arrangement, apart from the 

 zoooecia, by which the vibracular zooids are brought into 

 relation and their synchronous movements determined. 



1 have said that similar phenomena may probably have a 

 place in the history of other genera. Amongst the family 

 Selenariadce, Busk, the vibracula, we know, are developed 

 to an extraordinary extent, and attain a larger size than in 

 the genus Caherea. 



Their remarkable character, coupled with the fact that the 

 members of this group are free in their adult state, led Mr. 

 Busk to conjecture that these appendages might have a 

 locomotive function. And he informs me that this conjecture 

 has been verified by actual observation, and that some of the 

 Selenariadce at least do actually move about by means of 

 their vibracula. If this be so, it is in the highest degree 

 probable that those belonging to each colony act in concert, 

 and that their movements are, as in Caherea, simultaneous. 



However this may be, the case of Caherea Boryi seems 

 to be conclusive, as far as it goes. It may be considered 

 to prove that a nervous system, distinct from that of the 

 individual polypides, by which certain zooids in the colony 

 are brouglit into relation and common action, exists in one 

 instance, at least, amongst the Pohjzoa?- And this not un- 

 naturally leads to the inference that a similar system, 

 though perhaps in a less highly specialised form, may pro- 

 bably occur more widely in the class. 



It is not my purpose however to theorise, but merely to 

 direct attention to a very remarkable fact which has been 

 strangely overlooked, and its relation to the interesting 

 question raised by Fritz Miiller's investigations.^ 



^ It will be noticed that this goes much beyond the kind of communica- 

 tion between the various elements of the colony, which is supposed by 

 lleichert to exist, and for which iiis " commuuale Bewegungsorgan " 

 provides. 



- Since the foregoing was written I have seen Joliet's later researches on 

 the (supposed) Colonial nervous-system. [' Comptes Rendus,' Aug. 13th, 

 1877.] He finds it present in all the Polyzoa he has examined, and very 

 largely developed. It is composed of fusiform cells. At the expense of this 

 tissue, the polypide with its muscles is developed ; and in its bosom the ova 

 and the mother-cells of the spermatozoids are formec. He regards it as a 

 distinct, constituent tissue of the Polyzoon, which he proposes to call the 

 Eiidosarc. Its special function is the production of the polypides or the 

 reproductive elements. It is itself derived from the Endocyst. If these 

 conclusions are confirmed, they will form a very important addition to our 

 knowledge of the structural and physiological history of the Polyzoa. Put 

 they do not affect the significance of the fact to wliich I have directed 

 attention in my paper. 



