ORIGINAL COMMUNICATIONS. 



On the Development of Synapta inh^rens^ O. F. Miiller 

 (sp.) By Wyyille Thomson, LL.D., F.R.S.E., M.R.I.A., 

 F.G.S.^ Professor of Natural History, Queen's College, 

 Belfast. 



I HAVE had an opportunity during the past summer, 

 through the kindness of my friend Captain Wethered, of 

 observing with care some of the earlier stages in the develop- 

 ment of Holothuria inharens of O. F. Miiller, so well known 

 to microscopists from the remarkable character of its calcare- 

 ous armature. This singular Holothiu'id is abundant, buried 

 in mud bauks, at, and a little above, low water mark on 

 the shores of Belfast and Strangford Loughs. I had long 

 been most anxious to trace its mode of reproduction, but 

 every attempt, whether by sifting the surface of the water 

 with a towing net for a swimming larva, or by examining 

 the plants growing on the banks for an early creeping stage, 

 signally failed. In the mean time. Captain Wethered con- 

 trived thoroughly to domesticate three or four matui'e 

 Synaptse in a small tank ; and after they had been upwards 

 of a year in confinement, he was rewarded for his care and 

 patience by a brood of young. He was absent from home 

 for some days in the beginning of June of the year 1861, 

 and, on his return, he detected several extremely minute 

 transparent bodies moving on the surface of the glass of the 

 Synapta tank. On examining these with the microscope he 

 found that they were young Echinoderms, and, even at this 

 early stage, their mode of using their rudimentary tentacles 

 was so characteristic as to leave but little doubt of their 

 parentage. Captain Wethered kindly placed these embryos 

 at my disposal, and I examined them carefully from time to 

 time. There still, unfortunately, remains a doubt, whether 

 there may not be a still earlier condition of swimming larva. 

 The embryo, however, Avhen first observed, was extremely 

 minute (-8 mm. in length) ; its structure was very rudi- 



VOL. II. NEW SEU. K 



