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Show 472 MR. E. T. BROWNE O N [Mar. 17 belongs to the Gymnoblastic group of Hydroids. The Medusoid Willia stellata has been always considered a Leptomedusa and was placed by Haeckel among the Cannotidae. As I did not know of any clearly proved case of a gymnoblastic hydroid having a medusa which must be classified with the Leptomedusae, I examined by means of sections the exact positions of the gonads. It is one of the characteristic features of the Anthomedusae to have the reproductive cells on the wall of the stomach, and of the Leptomedusae to have the reproductive cells upon the radial canals. W h e n I first saw Willia I certainly regarded it as a Leptomedusa. At the base of the stomach six broad canals are given off; these run along a short peduncle and over the top of the sub-umbrella; along this portion the gonads are situated; at the point where the gonads terminate the canals suddenly decrease in diameter and become somewhat inconspicuous. Tbe question arose whether to consider the broad part of the canal upon which the gonads are situated as a prolongation of the stomach or as a part of the radial canal itself. To determine this point, I cut several series of sections of medusae belonging to the second and third stages. All the sections clearly show that the endoderm-cells of the stomach are continued, without any change in size or shape, along the whole length of that portion of the canal upon which the gonads are situated. At the point where reproductive cells terminate the canal suddenly decreases in diameter, and the endoderm-cells become very small and flat. I think that portion of the canal upon which the gonads are situated may reasonably be regarded as a prolongation or lobe of the stomach, and that the true radial canal commences at the end of this lobe. The sections also show reproductive cells at the base of the stomach itself, before it branches into the six lobes. I think this medusa is as interesting as the hydroid is remarkable. It shows a kind of transitional stage between the Anthomedusae and Leptomedusae. The continuation of the endoderm-cells, without change, into the lobes, and also the continuation of the reproductive cells from the base of the stomach itself along the lobes, strongly point to Willia belonging to Anthomedusae, and not to the Leptomedusae. D I S T R I B U T I O N :- Hydroid Form. England-Hfracombe, Hincks*. Medusoid Form. Scotland-St. Andrews, M'Intosh. Oban, Forbes. England-Plymouth, Garstang and E. T. B. Fowey, Peadi. Falmouth, Cocks. Penzance, Forbes. Hfracombe, Gosse. Ireland-Valencia Island, E. T. B. |
