THE CRASPEDOTE MEDUSA OLINDIAS AND SOME OF ITS NATURAL ALLIES. 11 



Some histological notes other than those mentioned heretofore may now be 

 added. 



The velum is very strongly developed, its mesoglcea is very thick in full-grown 

 examples, and on the subumbrellar side is thrown into numerous vertical folds, form- 

 ing muscular lamellse. The subumbrellar musciilature is also vigorously developed, 

 and there is a special muscular ring just inside the base of the velum, adjacent to the 

 nerve-ring. This is due to a special development of the muscular lamellae, which 

 are here very numerous and closely set, and are also exceptionally tall. The muscu- 

 lar lamellae are found here and there in all parts of the subumbrella, but they are 

 inconspicuous elsewhere. 



The nettle-cells are exceptionally large and cylindrical, and are in general form 

 like those of many actinians. When fully formed they are as large as 30 micra by 

 7 micra, and the protoplasmic mantle and the nucleus can always be distinguished 

 very clearly. The latter is usually found near the more slender end of the organ 

 and is frequently horseshoe-shaped. When the nettle-cells are placed in their defini- 

 tive position this slender end is invariably directed inwards, being the closed end of 

 the urticating vesicle. 



As before mentioned, the nettle-cells are comparatively few in the exumbrellar 

 tentacles, but are especially numerous in the ring-shaped warts of the velar tentacles, 

 and in these they are imbedded between exceedingly tall ectodermal cells, which are 

 very conspicuous in sections even under a low power. These ectodermal cells are 

 provided with veiy long stalks which stain deeply with haematoxylin, are more or less 

 undulating, and are attached below to the mesogloea. The body of the cell consists 

 of a granular or a somewhat fibrous cytoplasm with a distinct membrane and a deeply 

 staining nucleus situated near the centre. Under ordinary objectives the transition 

 between the stalk and the body of the cell appears sudden, but with a high-power 

 apochromatic system it is seen to be more gradual. These stalks were at first suspected 

 to be muscular in nature, but further observations revealed many transitional forms 

 between these and the ordinary tall ectodermal cells; and further, these stalks look 

 very different from the muscular fibres lying immediately below. It is evident, how- 

 ever, that the protoplasm of the stalks of these cells has undergone a special modifica- 

 tion, but its nature has so far remained obscure to me. These cells with deeply stain- 

 ing stalks are also present in the warts of the exumbrellar tentacles ; but they are less 

 nxmierous there and the stalks are shorter. 



Olindioides formosa has been observed in the following localities: Misaki; Kan- 

 agawa (practically identical with Yokohama, Prof. Mitsukuri) ; Bay of Tateyama, 

 southeastern extremity of the Bay of Tokyo (Dr. Oka). 



