50 ANATOMY AND PHYSIOLOGY OF SALPA AND PYROSOMA 



■diameter, which again frequently contained a round opake spot or 

 nucleus about Wo o * of an inch in diameter ; the latter sometimes 

 appeared as a thick-walled vesicle. This is plainly an ovum; a 

 narrow pedicle {q') is attached to its upper extremity and runs 

 upwards, curving slightly forwards to the same point as in the 

 preceding forms. 



It would appear then that the Salpa B developes a single ovum, 

 which is at first placed in the median line in the ventral sinus ; that 

 partly by the increase in size of the body, and partly in consequence 

 of a .shortening of its pedicle which acts as a gubernaculum, it 

 becomes drawn from this position upwards and to the left side ; and 

 that in the meanwhile, probably in consequence of fecundation, it 

 becomes altered in structure, and precisely similar to and identical 

 with the cellular mass which has been seen to form the rudiment of 

 the young Salpa A, Plate XVI. [Plate 6] fig. 7. In this case t/ie Salpa 

 A would be a true embryo developed by a process of sexual generation. 



34. Sexual generation however presupposes a male fecundating 

 organ, and this is found in Salpa B as a ramified body, hitherto 

 generally called a liver (/), Plate XV. [Plate s] figs. 6 and 7, closely 

 surrounding the intestinal canal with a network, solid in the younger 

 form, but in the older tubular, with very thin walls, and containing a 

 vast number of pale-greenish circular cells, from ToVuth to ^ Jyu-th of 

 an inch in diameter ; and besides these detached spermatozoa, with 

 very thin tails and long narrow heads, about y-gJijuth of an inch in 

 length. The testis has no visible excretory organ, but such might 

 well escape notice. 



Nothing at all resembling this body is found in the form A ; its 

 ■contents sufficiently demonstrate its real nature, and its existence on 

 the other hand is strong confirmatory evidence, if any be needed, that 

 the pediculate body described above is a true ovum. 



One curious circumstance needs to be remarked ; the testis does not 

 develope pari passu with the ovum and attain its full development at 

 the same time, as might be imagined. The testis is always behind 

 the ovum in its progress, and does not, indeed, seem to have attained 

 its full development until the latter has become freed from the parent. 



Without carefully tracing the form B through all its stages, it might 

 readily be supposed to be always male ; in fact, fully-grown specimens, 

 while they always possess a well-developed testis, rarely contain any 

 embryo, this being generally set free when the parent is about half 

 or two-thirds grown. The careful observer will, however, be always 

 able to detect a trace of its former attachment, in a sort of cicatrix, 

 left at the corresponding part of the respiratory chamber. 



