246 Observations on some joomis in ["CraZi, MayT^^a * 



attached by one extremity to the side of the vessel, and by the other 

 vibrating with a quick undulatory motion ui its cavity." * I have 

 watched with absorbing attention this undulating appearance, and 

 it is with much deference to such weighty evidence that I venture 

 to suggest the possibility of such an appearance to be an optical 

 illusion, and to be produced by a rhythmic contractihty of the vessel 

 itself ; in short, by a imlsation. 



Pulsation in the higher animals is due, if not to the direct 

 influence of the brain, to an independent nervous system of the 

 heart ; for the heart beats long after it has been severed from the 

 body, and any separated portion beats for a period so long as it 

 contains its own gangha ; separate such part however, from its own 

 gangha, and its pulsation at once ceases ; its stimulus is removed. 

 Then we have the perplexing statement that tJiere is no evidence of 

 nerves either in the embryonic heart, or in these pulsatile sacs of the 

 simpler animals. This, however, is but negative evidence ; no motion 

 can be produced without some agency, some stimulus to generate it ; 

 and as these peculiar motions occur in vessels which represent arteries, 

 and as the tissue of arteries is both contractile and elastic, in varying 

 degrees such rhythmic contractility will account for the pulsation in 

 the sacs, whatever may be the nature of the stimulus. 



Now what have we before us ? The arteries, if I may so call 

 them, pulsating at their connection with a fibre that runs off to the 

 brain, from the two processes that support both the ciliated belt and 

 the jpulsatile sac, and what is most interesting to observe, is a perfect 

 harmony between the rhythm of the sac and the beat of the cilia on 

 the belt. It therefore appears that the pulsations do derive their 

 influence from the brain, and further that, in the face of the accepted 

 singular fact of ciliary motion being " entirely independent of a 

 nervous system," it is also in this particular instance dependent 

 on such a stimulus, either directly or through the agency of the 

 coincident pulsations. 



The connection of the antennae with the vessels of the vascular 

 system is clearly apparent : these organs were first considered by 

 Ehrenberg, under the term " calcar," to subserve the generative 

 process as intromittent organs. He subsequently corrected this 

 notion, and promulgated the more reasonable one of theu' being 

 " respiratory tubes," through which water might enter to act on 

 the " vibratile tags." The correctness of this has been admitted by 

 Siebold and others ; but we read in Pritchard's resume that subsequent 

 researches "render such a conclusion untenable, and demonstrate their 

 analogy with the antennae of insects." Dr. Williamson mentions, in 

 respect to Melicerta, the fact of the inversion of the tube " forming 

 a double sheath protecting the setae," and ofi'ers this, with the inci- 

 dent of their being the first parts that make their appearance on the 

 animal emerging from its tube, in support of his deductions, but is 

 * 'Trans. Micro. Journal,' 1851. 



