Agassiz.] 22 [June 20, 



vanced, and he found it impossible to trace distinctly their mode of 

 junction. Soon after the chain escapes from the solitary form, while 

 still quite small, so that four or five individuals can be brought under 

 the focus at once, their peculiar arrangement is readily understood. 

 The chain (fig. 5) consists of two rows of individuals placed slightly 

 obliquely to the axis of the chain, in addition to the natural obliquity 

 of the individuals on the right and left sides. The ventral side is 

 always turned outside, and the individuals are placed therefore back 

 to back at an angle measured by the obliquity of the endostyles, which 

 is quite considerable. Besides this oblique arrangement of the ven- 

 tral and dorsal sides, the anterior and posterior extremities are not on 

 the same level ; the anterior extremity is tilted up so tliat all the an- 

 terior openings are brought to the upper side of the chain when it is 

 floating, and the posterior openings close to the edge on the lower side ; 

 the anterior opening is placed at a short distance from the edge of 

 the chain, thus bringing, by this arrangement, the anterior and poste- 

 rior openings on different sides of the chain. Adjoining individuals 

 are connected by the two large dorsal spurs of the anterior extremity 

 of the respiratory cavity. The next pair of individuals lap over the 

 first pair of the chain very considerably, so far that the nucleus of 

 the first pair is just below the nervous ganglion of the second pair. 

 The right individual of the anterior pair is connected with the Indi- 

 vidual immediately behind it by the small spur of the respiratory 

 cavity placed above the heart, and the large spur behind the nucleus, 

 while it (the right hand individual of the second pair) connects with 

 its adjoining fellow in the same way as In the anterior pair, and 

 with the left anterior one by means of the two small dorsal spurs of 

 the latter, and so on, for each succeeding pair, so that every individu- 

 ual of the chain is always connected by spurs to the three immedi- 

 ately surrounding it, in front, on the side and behind. 



As far as I have noticed, the chains remain connected till they are 

 full grown, although the breaking up of the chain from any cause 

 does not prevent the components from living for a short time, yet 

 the chain, as a whole, is by far more active than the separate compo- 

 nents when free. The largest chains I have seen are somewhat over 

 a foot in length ; in these the individuals measured about five-eighths 

 of an inch in length. This is much smaller than the solitary forms, 

 which attain a length of an inch. Sars and Krohn were the first to 

 repeat the observations of Chamlsso concerning the connection of the 

 BoUtary and aggregate forms, and they have clearly shown that the sol- 

 itary form is asexual, always producing by budding a chain of Salpse 

 which are the sexual forms, and bring forth but a single embryo 

 developed from an egg, giving rise to the solitary form. Huxley, 

 Leuckart, and Vogt, have also since shown the entire accuracy 



