WYVILL15 THOMSON,, ON ASTERACANTHION VIOLACEUS. 09 



seemed to be constantl}' searching the water around it for prey, 

 and occasionally to press the tentacles firmlv to the body 

 of the proboscis, as if to imbed some matter in the substance 

 of the latter. I ^yas unable to detect any opening at the summit 

 of the organ. 



As Ophryodendron now exists in great abundance in the 

 neighbourhood of seyeral eminent microscopic obseryers, Ave 

 must hope that its anatomy and mode of reproduction will be 

 worked out during the ensuing summer, and that it may be 

 discoyered in other localities. Claparede and Lachmann de- 

 scribe it as found on Campanularias ; but I haye never seen 

 it on any of that class of zoophytes, eyen when they haye 

 been growing intermixed with Sertidaria. I haye only found it 

 on one species of Sertularia, S. pmnila. 



On the Embryology of Asteracanthion yiolaceus (L.) 

 By Professor Wyyille Thomson^ LL.D., F.R.S.E., 

 M.R.I.A., F.G.S., &c. 



Sars^ in his wonderfiilly suggestiye ' Beskriyelser/ &c., 

 published in Bergen in 1835, threw the first ray of light 

 upon the structure of the singular provisional appendages 

 which have been since found to accompany the embryonic 

 condition of most, if not all, of the Echinoderms. We are 

 indebted to the same naturalist for several subsequent com- 

 munications on the same subject; the most important a 

 detailed description* of the early stages in the development of 

 Echinaster sanguhiolentus (Miiller), and a shorter notice of 

 the same process in Asteracanthion Mulleri (Sars). These 

 observations are so well known, that I need only refer to 

 them briefi3^ 



Sars found that in these two species the mode of repro- 

 duction conformed pretty closely to the usual invertebrate 

 type. Complete segmentation of the yelk took place, and 

 the greater part of the mulberry mass was then moulded into 

 the embryo Star-fish. 



The process presented, however, this peculiarity. A 



club-shaped appendage, with three or four 'short radiating 



processes, each terminated by a sucker, was developed from 



one part of the surface of the embryonic mass, and remained 



ched to the embryo during the earlier stages of its 



* ' Fauna littoralis Norvegise,' Pait i, Chvistiania, 1846, 



