Agaasiz.] 20 [June 20, 



per side to the opposite side, then running under it, and coming out on 

 the opposite side again, and stretching towards the median hne. The 

 young Salpce are all attached by the posterior extremity, exactly as we 

 find colonies of fixed Ascidians and Bryozoans, to a tube, (</. t.) which 

 is a simple diverticulum of the circulatory system, and freely communi- 

 cating with the gemmiferous tube as it is called. The young Salpse are 

 not uniformly developed in proportion to their distance from the base 

 of the tube. Sections of the tube are equally advanced, and we 

 find generally three such portions unequally developed, as has been 

 noticed by Sars, Krohn, Huxley and others. The base of the gem- 

 miferous tube is simply sUghtly corrugated, next comes a section in 

 which we find two rows of slight elevations, and finally the most 

 advanced part of the chain where the rudimentary Salpae are more 

 or less advanced, and resemble in every respect, long before it be- 

 comes detached, the chains which are found floating about. These 

 sections are thus liberated in turn, new ones continually forming 

 at the base of the gemmiferous tubes during the budding season. 

 The part of the chain which is the most advanced occupies, however, 

 so much of the tube that the other sections are scarcely noticed. These 

 chains escape through an opening formed at the proper time through 

 the tunic, near the nucleus, on the ventral side, which shows after- 

 wards no trace of the passage of the small chain. When the solitary 

 SalpfE are kept in confinement for any length of time, nothing is more 

 common than to find floating about diminutive Salpas chains, nearly 

 identical in every respect, except size, with the larger chains found at 

 the same time in the sea. These small chains usually consist of from 

 twenty to twenty-eight pairs ; they increase rapidly in size, as we find 

 them of all sizes during every month in which Salpae have been 

 noticed, from the chains just escaped to the largest, which have 

 already lost their solitary embryo. The mouth is placed beneath the 

 heart, at the upper extremity of the posterior part of the gill ; it 

 opens into a kind of oesophagus, and the winding course of the 

 dio-estive cavity can readily be followed in specimens which have 

 lost the chain of Salpte ; the anus opens close behind the mouth in 

 the respiratory cavity. The pyriform tubes first noticed by Huxley, 

 are readily seen in the solitary specimens, though they are more 

 plainly observed, as well as the eleoblast, in the aggregate form, just 

 after their escape from the solitary Salpae. 



The principal difierence between the solitary and aggregate forms 

 is one of outline, and in the proportion of the diflerent organs, which 

 are essentially the same, except the organs of reproduction. The 

 individuals of the chains are all alike on one side, that is, we find the 

 endostyle either slightly to the right or to the left of the median line, 

 according as the individuals are on the right or left row of the chain. 



