OF TUBULAR AND CELLULAR POLYPI, AND OF ASCIDIiE. 375 



beyond the separation. Still later the current extended from the root along a part 

 only of the line of pulp in the stem ; a vortex was established where the stream 

 ended, and the pulp beyond that part assumed a larger granulation ; the root being 

 the place where the remains of life were latest retained. 



The drawings of Plate X. fig. 1. may, like the last, be referred to Ellis's pi. xxxviii. 

 3 B. He there represents young polypi as emerging from ovaries ; and states, in the 

 French edition of his work, that they appeared evidently to spread their tentacula ; 

 and that some, becoming detached, sank to the bottom of the glass of water in which 

 they were placed, where they began to move and extend, like the freshwater polypi. 

 Cavolini, on the other hand, watched in vain to witness the exclusion of the ova ; 

 but he produces experiments and arguments, from which he infers that the young 

 polypi of Ellis were imaginary, and that the ova, when first given out, have no 

 external organs or sensibility, but resemble the seeds of plants, with a scabrous 

 surface to enable them to adhere to bodies *=. 



When my specimen was subjected to the microscope (July 20, 1833), a kind of 

 tube or hollow cord of granular matter could be seen, more or less distinctly, ex- 

 tending through each of its ovaries from the base, generally along the axis like the 

 columella in plants, and having the ova attached to it. These, in some ovaries (as 

 «,) were small, and the cord spread out into a substance that filled up the end, 

 indicating, by its appearance, that the shell was there not yet completed ; in others 

 (h,) the substance at the end was shrunk, and the ova were grown larger ; in others, 

 again, the foremost ova reached the end, and had an appearance of maturity ; those 

 behind were always less advanced. 



The ova were roundish, and consisted of two portions ; the outer and more trans- 

 parent, that might be called the white, inclosing an inner bag filled with particles 

 in fluid like those in the currents of the stem and connected with them by the cord. 

 The current and agitation were Seen in the inner bags only, and the flow into and 

 from them alternately along the cord was strongly marked. When near the end of the 

 cell, the ova became more opake, which hid the changes that might be taking place 

 within them. The number in a full ovary was about seven. Their expulsion took place 

 from several with much the same circumstances, of which the ovary marked h may 

 give an example. In two days after that tracing was made they had filled the shell 

 to the end, and began to emerge in succession at an average interval of six hours. 

 The protrusion {h 2, h 3) took about a quarter of an hour, and was commonly pre- 

 ceded by a transparent projection, like torn membrane, before the end of the ovary, 

 and a few active particles in the water. 



Each young polypus was at first an oval body on a very short pedicle, and ap- 

 peared dark from being filled with opake particles, generally smaller than those 

 in circulation, which were in great and continual agitation and seemed to have no 



* Dr. Grant, in his observations on the ova of various zoophytes, (Edinburgh New Philosophical Journal, 

 vol. i. p. 150,) concurs in the opinion that Ellis was in en'or. 



3 c 2 



