MORPHOLOGY. 19 



sacs with a gonocalyx ; then that gonocalyx becomes a well-developed contractile organ ; next 

 the reproductive apparatus is detached, and swims about independently by means of its gonocalyx 

 or umbrella; andjfinall)^, it acquires total independence, feeding and nourishing itself, and attain- 

 ing the most complex organization exhibited by the class to which its originator belongs. 



Even this, however, is not the whole extent'of specialization attained by the reproductive 

 system in the ITi/drozoa, for, in certain members of the class, the reproductive organs, 

 or zooids, themselves are developed from, or in, organs especially devoted to that object. 



Thus, among the Coryn'uJce, the gonophores of Ilydractitiia echinafa are developed neither 

 from the ordinary polypites nor directly from their connecting coenosarc ; but the latter gives 

 rise here and there to cylindrical processes [Mastosfi/les), each of which is about as long as a 

 polypite, but is terminated distally, not by a mouth, but by a pyriform enlargement, which 

 gradually diminishes to a point, and is covered with small, irregular lobes or tubercles. 

 The circumference of the widest part of the enlargement is produced into ten or twelve 

 such particularly well-marked conical enlargements, which are thickly beset with thread- 

 cells. From the stem of the process below these, the gonophores are developed, and from 

 its base there arises a short, cylindrical body, dilated at its extremity into a globular head, 

 full of minute, dark reddish orange granules. At first sight this body looks very like the 

 lithocyst of a Ci/an(sa, but I have been unable to find evidence of its possessing a similar 

 structure. 



Some Sertulariadm exhibit organs similar in principle to these, though differing in the 

 details of their structure. Thus, pedunculated, urn-shaped bodies rise from the coenosarc 

 of Laomedea gelatlnosa. The peduncle has the same structure as the coenosarc, containing a 

 central canal, and having the cuticular layer of its ectoderm more or less distinct from 

 the deeper substance. Where the peduncle enlarges into its urn-like dilatation, the walls of 

 the latter may be clearly seen to be continuous with this cuticular layer of the ectoderm only ; 

 at the distal end of the urn its walls turn abruptly inwards on all sides, thus forming 

 a concave face, tlie middle of which is produced into a short, spout-like, open mouth. 

 The continuation of the rest of the substance of the peduncle (consisting of the inner moiety 

 of the ectoderm, with the whole endoderm, and their contained cavity) traverses the axis of 

 the urn nearly to its end as a sort of columella — the blastostyle of Allman — but its termination 

 is hidden by the mass of buds in advanced stages of development which are clustered round it. 

 These buds may be traced down the sides of the blastostyle, until, at the base of the urn, they 

 are to be detected in their primary condition of caecal processes of its wall. Each eventually 

 acquires the form of a " Medusa," with marginal tentacles and lithocysts, and leaves the 

 theca by its superior aperture to swim about by itself, and eventually develope the repro- 

 ductive elements. 



The relation of the reproductive organs of many Fhi/sophoridee to the peduncles of those 

 pecuHar csecal polypiform bodies described above under the name of hydrocysts, or, as in 

 VelelJa, to true polypites, is very similar to that between the reproductive organs of 

 Hydracthiia^ and their support, or between the budding medusiform zooids of Laomedea and 



* Vogt (p. 133) and Leuckait (Z. U., p. 16, and Z. N. K., p. 71) have already drawn attention to 

 this resemblance, and have included, under the common term of " proliferous individuals," not only these 

 bodies, but the small polypites of the Velellida. 



