NERVOUS SYSTEM OF THE POLYZOA. 301 



The demonstration of this nervons system^ it is true^ will be 

 excessively difficult in the majority of the Polyzoa; the diffi- 

 culty of course being increased in proportion with the diminu- 

 tive size, greater amount of calcareous matter, and consequent 

 want of transparency in the test, and diminished under the 

 opposite conditions. In this respect there cannot perhaps be 

 a more favorable subject than a species of Serialaria, by no 

 means rare in the sea of Santa Catharina, whose polyzoary 

 consists throughout of thin-wallcd, almost perfectly transpa- 

 rent joints or internodes, an inch or more in length. In this 

 species, in fact, a general or common nervous system is more 

 plainly manifest than I remember elsewhere to have met witii, 

 except in the case of the Salpce. 



As the sole object of the present paper is the exposition of 

 this system of nerves, I shall confine myself, in describing the 

 animal, simply to the particulars necessary for the recognition 

 of the species and the due understanding of what follows, and 

 shall, therefore, pass over the intimate structure of the poly- 

 pide. The branched polyzoary of Serialaria Couiinhii, Miill, 

 spreading on seaweeds over a space of three or four inches, is 

 composed of cylindrical joints, which attain a length of more 

 than 40 mm., and a breadth of 1"35 mm., the successive 

 joints gradually diminishing in thickness until the terminal 

 twigs are not more than O'l in diameter. The branches divide 

 trichotomously, in such a manner that from the extremity of 

 each branch three twigs of unequal size arise, the two thicker 

 ones being continued in nearly the same plane with the pri- 

 mary branch, whilst the third and smaller one stands at an angle 

 of about 60° with the others. The mode in which this kind 

 of branching arises is readily seen in the extreme ramifications 

 of the polyzoary. At the extremity of a branch, in the first 

 place, a solitary bud arises, forming, as it were, simply a con- 

 tinuation of the branch (PI. XI, fig. 1 a) ; but this is subse- 

 quently pushed more and more to one side (fig. 1 a) by a second 

 bud (fig. 1 b), which soon makes its appearance close to the 

 former, the angle betAveen the branches thus formed often 

 exceeding 120°. The third, still younger branch (fig. 1 c), 

 arising between the other two, and growing in a direction per- 

 pendicular to the plane in which they lie, usually does not per- 

 ceptibly interfere with their direction, so that they remain 

 pretty nearlj^ in the same plane with the primary branch. 

 Occasionally, though in all cases at a much later period, and 

 long after the former branches have already themselves 

 become branched, a far smaller fourth branch makes its 

 appearance opposite the third (fig. 1 d), and very rarely 

 even a fifth may arise, but I have never seen the number to 



