Observations on Britisli Zoophytes, 



43 



On examining a specimen of Stomobrachium last summer, 

 which bad been recently fed on tbe wbite part of an oyster, 

 I noticed (fig. 1 a a a) a retiform system of fine canals, 

 wbich permeated tbe muscular web of the sub-umbrella, and 

 was altogether distinct from the eight large lateral canals 

 which carried the ovarian bands. This canal system con- 

 sisted of from three to five fine tubes, which sprung from 

 the upper part of the peduncle, between each of the lateral 

 canals, and passed outwards and downwards as a rarely anas- 

 tomosing network, to join the circular canal bordering the 

 mouth of the bell. No branches from it joined the lateral 

 canals, as the latter were bordered on each side by the long- 

 ovarian bands. Tbroughout the whole supplementary system 



in water recently brought from the sea. It must be slowly filtered through 

 blotting-paper into a glass vessel capable of containing not less than three 

 or four gallons, in which are placed a few fronds of Chondrus crispus, Entero- 

 morpha or Ulva. A few Medusa? only should be placed in the vessel, and fed 

 with very small pieces of mussel. 



As soon as the planulaj appear they should be removed with a dipping- 

 tube into a round glass shade inverted and filled with filtered sea-water from 

 the larger vessel, to which a few drops of mussel-juice must be added daily, 

 until it appears crowded with minute protozoa. The internal surface of the 

 glass, and especially the surface of the water, should be examined daily from 

 without with an inch lens, and as soon as each planula adheres to the inside 

 of the glass, a thin cover of microscopic glass should be attached externally 

 over its site with an interposed drop of glycerine, to ensure a flat surface, 

 and the microscope, placed on a proper support, should be brought up to 

 it. The light, the quantity of which must be regulated by a diaphragm 

 of black paper, should be reflected from a plane mirror, and carefully adjusted 

 to pass directly in the axis of the tube of the microscope. By this means 

 the whole process of the development of the planula into the hydroid 

 zoophyte, with the successive budding of the polyps, may be seen in a 

 very beautiful manner. This process is carried out in a period varying 

 with the genus from which the planula is derived. Thus, in Sertularia 

 pumila and Campanularia dichotoma, the first young polyp is complete in 

 a few hours ; while in Hydractinia and Equorea, our patience is tried 

 for several weeks ere the same event occurs. The planula of the Stegan- 

 opthalmata, such as Chrysaora, Cyanea, and Aurelia, may be removed from 

 the ovaries or marsupial sacs of the Medusa? as they lie exposed on the sea 

 shore, and rarely fail to become developed into polyps or Ephyras. In this 

 phase of their development they remain for many years, if well fed and kept 

 in a darkened place, and multiply rapidly by gemmation. They may, how- 

 ever, be forced to assume their medusoid phase, by exposing them, without food } 

 in a small quantity of sea-water, to direct sunlight. 



