ANATOMV AND PHYSIOLOGY OF SALPA AND PYROSOMA 45 



The blood, in its alternate flux and reflux, bathes all the internal 

 organs — the intestine, the endostyle, the brain and the generative 

 organs, the corpuscles finding their way as they best may among the 

 interstices. When the force of the heart diminishes, they frequently 

 accumulate around the intestine in consequence of becoming en- 

 tangled among the meshes of the areolar tissue (13) connecting the 

 intestine with the parietes. 



21. So far, the structure of the two forms A and B has been 

 identical ; but in proceeding to examine the reproductive organs, it 

 will be necessary to treat of each separatel}^ 



The form A is alwaj^s found to possess a connected series of young 

 forms, the so-called Salpa chain, encircling its visceral nucleus ; the 

 form B, on the other hand, never possesses the Salpa chain, but 

 generally contains a solitary foetus, pendent from the upper and 

 posterior part of its respiratory cavity. It is clear therefore that 

 in each of these forms reproduction takes place. But is the mode of 

 reproduction in each case similar or different ? Are both, processes 

 of gemmation, or processes of sexual reproduction, or is one process 

 of the one description, the other of the other description ? To come 

 at the solution of this question, it will be necessary to know first, the 

 nature and relations of the chain of young in A, then the nature and 

 relations of the solitary foetus in B, and, finally, to trace back the 

 development of both to their first origin. 



22. Salpa chain of A (Plate XV. [Plate S] fig. i /i. Plate XVI. 

 [Plate 6] fig. I. Plate XV. [Plate 5] fig. 9). The chain is formed 

 of a double series of foetuses, commencing on the right side of 

 the nucleus, curving under it, then turning upwards and over it to 

 the right side, and finally terminating in the middle line by a free 

 extremity midway between the two long posterior horns. 



The chain is enclosed in a proper cavity, hollowed out in the sub- 

 stance of the outer tunic, and this sometimes opens externally 

 opposite the free extremity of the chain, Plate XV. [Plate S] fig. 9. 



23. The foetuses do not form a chain by mere apposition ; they are 

 all attached by pairs to one side of a cylindrical double-walled tube, 

 which is connected, at its anterior or proximal extremity, with the 

 system of sinuses of the parent, to the right of the heart. The tube is 

 in fact merely a diverticulum of the sinus system, Plate XV. [Plate 5] 

 fig. 9, and the blood contained in the sinuses passes freely into it. It 

 is divided by a partition (j) into two canals, which are distinct for 

 the whole length of the tube, except at its very extremity, where they 

 communicate just as the two seals of the cochlea do ; and it thence 

 happens, that in the living animal, a constant current passes up on one 



