330 BULLETIN OF THE 



The zooid3 which compose the set nearest the proximal end of the 

 tube are very much smaller than those of the second, which again are 

 sharply distinguished from those of the third, and so on ; and at a 

 time when the first are very rudimentary indeed the last present 

 all the organs of the adult, with the exception of the testis, and are 

 ready to be discharged into the water. The carefully drawn, but 

 somewhat rudely engraved figure of the fully developed chain, given 

 by Eschricht,* gives an excellent idea of the position and relations of the 

 various parts at this stage, and is, by far, the best figure which has ever 

 been published. The position of the zooids is uniform throughout all 

 parts of the stolon. The incurrent openings of all are upon the con- 

 vex, and the excurrent upon the concave or inner side of the tube. 

 The zooids of the opposite sides alternate with each other, and 

 their h&mial surfaces face inwards. They are not perfectly parallel, 

 for the visceral ends of their bodies are nearer each other than the 

 neural ends, which incline outward. Fig. 34 shows a few zooids from 

 a set which is nearly large enough to be discharged. The young 

 chain, when first set free, is about half an inch long, and the single 

 zooids, of which there are from twenty to thirty on each side, meas- 

 ure about one tenth of an inch in length. They grow very rapidly 

 and soon reach their full size, when the chains "are often a foot or 

 even a foot and a half long, and contain two rows of individuals, which 

 are united together in such a way that they stand obliquely to the axis 

 of the chain; the branchial openings are all on the upper side of t lie 

 chain as it floats in the water, while the posterior openings are all 

 on the lower side of the chain, close to the edge. Each individual is 

 connected both with its mate on the right or left side, and to those 

 immediately in front and behind on the same side. The succeeding 

 individuals in the chain overlap considerably. The chains do not 

 appear to break up spontaneously, but when broken apart by accident, 



the individuals are capable of living separately for several days 



The individuals composing the chain, when full giuwn, are about three 

 epiarters of an inch long."t I do not think that the separation of the 

 zooids makes the least difference in the length of their life, and the 

 full-grown chains fall apart at the slightest touch, and, unless the 

 water has been perfectly still for several days, chains more than four 



* Undersogelser over Salperne, Tali. IV. 



f Verrill, Invertebrate Animals of Vineyard Sound (p. 447;. 



