CIRCULATION OF THE BLOOD IN PYROSOMA. 281 



tion of the current, and then 33 j)ulsations ; then 133, 68, 

 139, 48, 28, 68, 38, 27, Sec, with uncertain oscilhitions 

 before or after the pause. It is necessary to remark tliat this 

 uncertainty in the number and duration of the pulsations is 

 observed less in individuals which are lively, and only just 

 extracted from the Pyrosoma colony ; moreover, if the water 

 is from time to time changed, the current slackens at once. 

 At last, the four embryos, having become adult and fully 

 organized, remain alone. In the vascular cord which united 

 them the movement of the blood ceases, and it diminishes, 

 becomes atrophied, and only a few globules of the blood 

 remain stationary and visible in the vessel of the interior of 

 the body. The heart of each embryo now acts separately, 

 and the circulatory apparatus is reduced to a great blood- 

 sinus between the external and internal tunic, the latter 

 being a little depressed at the poles of the embryo, and the 

 sinus here becoming somewhat larger. The heart forces the 

 blood into the sinus, and also into the little canals which 

 exist between the branchial clefts, and in these cilia are now 

 for the first time seen. I have several times seen the blood- 

 globules traverse them slowly, one after another, through 

 the whole length, and reappear at the extremity, to he 

 poured into the general sinus, and was able also to verify 

 this fact in the preceding stage of development, that is to say, 

 when the vascular union between the embryos was still exist- 

 ing, but in this case the ciliary movement had not yet 

 appeared. It is to be noted that, in consequence of the dis- 

 position of the parts of the embryo, the transverse elements 

 of the branchiae — that is to say, the clefts and the interposed 

 canals — are placed in the direction of greatest diameter ; by 

 the elongation of the region of the mouth, these elements 

 ultimately take their natural position. 



It is known that, besides sexual generation, Pyrosoma pre- 

 sents contemporaneously a reproduction by buds, as was dis- 

 covered by Professor Huxley, and seen also by Messrs. 

 Keferstein and Ehlers. The embryos develope one after 

 another on a peduncle or tube, Avhich projects from beneath 

 the end of the endostyle of the adult Ascidian, opposite to 

 the heart, and is formed from its external tunic. Mr. 

 Huxley has already pointed out that there is a vascular com- 

 munication between the mother Ascidian and the embryos, 

 which commences by a deflection of the blood-sinus of the 

 Ascidian, and is continued to the neural surface of the em- 

 bryo ; and he states that it does not cease to exist until after 

 considerable time, when the embryos are completely deve- 

 loped. I have seen that these budded embryos possess a 



