the Ova of Zoophytes. 155 



undergoing the least change of form ; on cutting an ovum of the 

 Sp. papillaris transversely through the middle, its anterior half 

 continued the motions of its cihae for 24 hours. The form of 

 the ovum, and its general appearance, vary with the species, and 

 are as easily distinguishable as those of the adult. Having now 

 examined these ova during two successive years, and having 

 varied my experiments in every possible manner, I consider 

 the spontaneous motions of the ova in the above species as suffi- 

 ciently established by direct observation, and by the analogy of 

 other zoophytes. 



The observations which I have lately made on the ova of tlie 

 Plurnularia Jalcata Lam., have not been less satisfactory than 

 those so often repeated on the ova of the sponge. I have taken 

 the mature ova from the vesicles of the plumularia, and examined 

 their spontaneous motions, under the microscope, in the presence 

 of experienced naturalists ; and I now present to the Wemerian 

 Society eight of these ova growing and branching on the side of 

 a glass vessel, after their having remained three weeks in that 

 situation. This species is very common in the deeper parts of 

 the Frith of Forth ; its vesicles are very numerous, and its ova 

 are in full maturity at the beginning of May. The ova are 

 large, of a light brown colour, semi-opaque, nearly spherical, 

 composed of minute transparent granules, ciliated on the surface, 

 and distinctly irritable. There are only two ova in each vesicle ; 

 so that they do not require any external capsules, like those of 

 the campanularia, to allow them sufficient space to come to ma^ 

 turity. On placing an entire vesicle, with its two ova, under 

 the microscope, we perceive, through the transparent sides, the 

 ciliae vibrating on the surface of the contained ova, and the cur- 

 rents produced in the fluid within by their motion. When we 

 open the vesicle with two needles, in a drop of sea-water, the ova 

 glide to and fro through the water, at first slowly, but afterwards 

 more quickly, and their ciliae propel them with the same part 

 always forward. They are highly irritable, and frequently con- 

 tract their bodies so as to exhibit those singular changes of form 

 spoken of by Cavolini. These contractions are particularly ob- 

 served when they come in contact with a hair, a filament of con- 

 ferva, a grain of sand, or any minute object ; and they are like- 

 wise frequent and remarkable at the time when the ovum is bu- 



