314 Botanical Society of Edinburgh. 



the form of a half-developed medusoid, never becoming detached, 

 but forming the embryo in that position. In the third species, the 

 medusoid was completely developed, and escaped freely into the 

 water. Certain points of resemblance, and their single mode of 

 origin, left no doubt in his mind that the medusoids in the case of 

 C. volubi/is were only a more highly developed form of the " ova" 

 observed in C. gelatinosa, the extreme forms connected by the unde- 

 veloped medusoids of C. geniculata. It is possible that these three 

 forms of reproduction may not be characteristic of the three species, 

 but may be common to them all under certain modifying circum- 

 stances. Dr. Thomson then mentioned the distinction so broadly 

 drawn between the " ovum," the product of the true generative 

 process, and the gemma or bud. He suggested that the ovum might 

 be perhaps considered more properly a gemma separated from the 

 parent, and capable of attaining a greater or less development, and 

 that the definition now generally applied to the ovum might be 

 attached to the embryo in its early stages. 



The conclusions to which the author seemed inclined to arrive, 

 were, — 1. That the medusoids were, in their least developed form, 

 closely allied to the ovarian ovum in the higher animals. 



2. That these medusoids, thus resembling the ovarian ovum, might 

 be considered as being produced by a process of gemmation from the 

 parent, and that as free gemmae they had the power of attaining a 

 considerable degree of development in some species. 



3. That these medusoids closely resembled the ovules in plants in 

 their structure and in their mode of development, and that, like ovules, 

 they were sometimes entirely absorbed by the growing embryo while 

 within their capsule, and were sometimes extruded from the capsule 

 when the embryo was extremely small (or even before impregnation?). 

 This property they of course possess in common with the ovarian 

 ovum in higher tribes. 



Dr. G. Johnston of Berwick stated, that he differed from Dr. 

 Thomson in regarding the development and reproduction of Zoophytes 

 as indicating an analogy with these processes in plants. 



Professor Edward Forbes said, that Dr. Thomson's paper referred 

 to some of the most debateable points in zoology, and that this was 

 not the place to discuss them. He thought that Dr. Thomson had 

 not kept in view the difference between analogy and homology, in 

 drawing a comparison between the zoophyte and the plant. 



3. " Notes of a Tour in Switzerland," by John Sibbald, Esq. 



4. " Notice of the Discovery of Hieroehloe borealis, near Thurso," 

 by Robert Dick, Esq. Mr. Dick stated, that at " about ten minutes' 

 walk from the town of Thurso, there is, by the river-side, a farm- 

 house known by the name of the Bleachfield, opposite to which, on 

 the eastern bank of the river, there is a precipitous section of boulder 

 clay ; opposite to the clay cliff, and fringing the edge of the stream, 

 any botanist can, in the last week of the month of May, or in the 

 first and second weeks of June, gather 50 or 100 specimens of Iliero- 

 chto'c borealis. Passing upwards along the river bank, and at no 

 great distance, there is another clay cliff, where a few hundreds of 



