DEVELOPMENT OF FLANULA IN A PLUMULARIAN HYDROID. 83 



On the Development of the Planula in a Certain 

 Species of Plumularian Hydroid. 



By 



Ernef^t Wavreii, D. Si*. (Loud.)* 



With Plate VI and 4 Text- figs. 



The development of the planula in this hydroid is note- 

 worthy in that the egg never becomes charged Avith yolk. 

 The ovum remains small and segments in the midst of a feed- 

 ing or placental tissue. Ultimately the embryo grows into a 

 well-developed planula with dimensions very greatly exceeding 

 those of the original egg. 



Some brief notes on the subject were communicated to the 

 South African Association for the Advancement of Science at 

 the annual meeting held in Louren^o Marques, July, 1913. In 

 the present paper the necessary details with drawings are 

 given, and the species of hydroid is described. 



The hydroid was found in January, 1911, in a rock-pool on 

 the north side of the mouth of the St, John's River, Pondo- 

 land. Only two clusters were gathered, and they both 

 occun-ed on the shells of living oysters much incrusted with 

 the calcareous tubes of Serpula, The upright pinnate stems 

 were about ^ in. in height. 



Trophosome. — Hydrorhiza consists of an irregularly 

 branched stolon, which in the present specimens was creep- 

 ing among the tubes of Serpula covering oyster-shells (text- 



