ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA 47 



adhered together in a single series, the left antero-lateral extremity of 

 the one being appHed to the right postero-lateral extremity of the 

 other ; and when they became free the traces of the connection were 

 visible as angular processes of the sinus system. 



It is not correct to say that the Salpa chains have organs of attach- 

 ment. At first they are attached by the whole length of their lateral 

 faces, the sinus system of one being continuous by a wide channel 

 with the sinus system of the other ; but as they grow these communi- 

 cating channels become more and more narrowed until they are mere 

 points of connection ; all communication then ceases, and the Salpa 

 become free from one another and move about independently. 



27. Having thus determined the nature and relations of the Salpa 

 chain, it remains only to be said, that the young when freed, have a 

 sub-ovoid, posteriorly-pointed form, five muscular bands, facetted 

 sides, and in short are identical in form, and ultimately in size, with 

 the form described as Salpa B. One-half, therefore, of Chamisso^s 

 theory is clearly correct ; the solitary Salpa (Salpa A) produces the 

 aggregate form (Salpa B) ; and we may add, that this takes place by a 

 process of gemmation from the walls of a tube in free communication 

 zvitk the circulatory system of the parent. 



28. Solitary Fcetus of Salpa B. — Whilst this form still forms part of 

 the chain or is but just freed, it is sure to contain a solitary foetus ; 

 and frequently one may be found in it when it has attained its full 

 size, but as often not. 



When the solitary foetus exists, it hangs freely in the respiratory 

 cavity (Plate XV. [Plate 5] figs. 4, 8) by means of a pedicle attached 

 to the upper and posterior part of its wall, on the left side of the 

 mouth of the parent. In its youngest and most rudimentary state 

 it is a somewhat conical papilla (Plate XV. [Plate 5] fig. 7) or 

 bulging of the inner tunic, consisting of an inner oval or pyriform 

 cellular mass, enveloped in a delicate transparent membrane, which 

 appears to be a continuation of the inner tunic. 



As development proceeds the inner mass becomes divided into two 

 portions, a larger turned towards the respiratory cavity, and which 

 projects more and more into it, and a smaller subspherical, turned 

 towards and lying in the cavity of the sinus, and bathed by the 

 parental blood. 



29. The whole mass goes on enlarging, but the former portion 

 faster than the latter. The former becomes somewhat ovate, with 

 its long diameter in the same direction as the long diameter of the 

 parent, and gradually assumes the form of a Salpa. The muscular 

 bands, the gill, the ganglion and its otolithic sac become distinct, and 



