POLYPI. 129 



In a third species of Tubularia (T. Dumortieri) the embryo 

 assumes the form of a transparent, gelatinous, longitudinally ribbed 

 Beroii, before it escapes : and afterwards moves like a IMedusa by 

 alternate contraction and expansion of the body. The change of 

 tin's medusoid larva into the Tubularia was not seen. 



In the Hydractinia rosea V. Beneden found several ova, with 

 the germinal vesicle and nucleus, developed in each ovicapsule. 



The modification in the gi'owth of the coralline to form the ovi- 

 capsule, has been compared by Professor E. Forbes* Avith that "me- 

 tamorphosis in flowering plants in which the floral bud is constituted 

 through the contraction of the axis and the whorling of the indivi- 

 duals borne on that axis, and by their transformation into the several 

 parts of the flower." Many elegant varieties are observable in the 

 form of the ovicapsules. Sometimes they are crossed by transverse 

 bars ; sometimes shaped like a vase, and provided with a little lid or 

 cover; usually traversed along the middle by a continuation of the soft 

 tissue of the polype, from which the ova or germs proceed, and which 

 may be compared to an umbilical cord, and is termed the " placenta- 

 rium." According to the botanical analogy, they may be either 

 essentially " single individuals, ideally metamorphosed into repro- 

 ductive organs comparable to the monocarpous germens of plants/' 

 or a "series of individuals joined together and merged into each 

 other so as to present the appearance of an organic body in which 

 the ova are reproduced comparable to the syncarpous germens" of 

 plants ; the pod-like ovicapsule of most PlumularicB well illustrates 

 the latter view.f 



Ehrenberg \ regarded the ovicapsule as a modified individual, viz., 

 a female generative polype, differing from the nutrient and sexless 

 polype, in having the tentacula rudimentary or abortive. The 

 contractile power of the ovicapsules in Pennaria and in Syncoryne 

 ramosa, together with Lovcn's description of the deciduous nursing- 

 polypes developed from the ovicapsule in the Campanularia geni- 

 culata, gave apparent support to this view, which, however, later 

 facts as to the nature of the progeny developed in the ovicapsule 

 have induced most zoophytologists to abandon. 



Sperm-capsules, similar in situation and form to the ovicapsules, are 

 developed in certain individuals of the marine ITydrozoa. In Pennaria 

 Cavolini the spermatozoa are developed in the interspace between the 

 inner wall of the sperm-capsule and an axial cord of the soft tissue 

 answering to the placentariura of the ovicapsule.§ In the Tubularia 



* ex. t XCVII. pi. 11. B. (Plumuhria falcata.) 



X CXVII. § CXVI. p. 197. 



K 



