154 Dr Grant mt the Sponta?ieous Motions of 



the microscope, they exhibited the same granular structure 

 (Cav. Abhand. p. 50.) The detailed account which Cavolini 

 has given of the spontaneous motions of the ova in these two 

 zoophytes, agrees so remarkably with what I have observed in 

 other genera, that I have not the least doubt that they are pro- 

 duced in the same manner, by the rapid vibration of minute ci- 

 lia distributed over their surface ; and that the cihae have 

 escaped his observation, and that of Mr Ellis (in the Campami- 

 laria) only from their not employing the high magnifying 

 powers necessary to render them distinct. 



In a memoir on the Structure and Functions of the Sponge, 

 read to the Wernerian Society, in March 1825, I described the 

 singular motions which I had observed in the ova of the Spongia 

 panicealLam., Sp. papillaris, cristata,tomentosa, between the time 

 of their expulsion from the fecal orifices, and that of their perma- 

 nently fixing themselves to develope on the surface of watch-glass- 

 es, and represented the appearance of the cihae which I had disco- 

 vered by the aid of the microscope, vibrating on the surface of the 

 ova as they moved about in the water, and even for a short time 

 after they had fixed themselves (see Edin. Phil. Journ. vol. xiii. p. 

 382.) The details connected with the formation and detachment 

 of these ova, their structure at the time of expulsion, and the 

 changes they undergo during the fixing and developing of their 

 bodies, are reserved for the continuation of my memoir on that 

 animal ; but, with reference to their spontaneous motions, I may 

 here observe, that they are all somewhat egg-shaped, the cih'ae 

 cover every part of their surface, excepting their posterior ta^ 

 pering extremity, where I have never distinctly perceived them. 

 In swimming, they always carry their broadest extremity for- 

 ward. They have a granular structure, and a rough surface, 

 like the ova of the gorgonia ; but spicula are distinctly discerni- 

 ble in those of the Spongia panicea, at the time of their expul- 

 sion. They do not change their forms, while swimming, like 

 the ova of many other zoophytes, but ghde along with a regular 

 and smooth motion. After remaining some time in the water, 

 they generally come to the surface, and collect round the mar- 

 gin. When one of them is placed in a drop of water, under the 

 microscope, we often see the motions of the ciliae gradually 

 cease, and become again suddenly revived, without the ovum 



