. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 1196 TUNICATA. mogeneous structure crowded with " nuclei" and bloodvessels, and only occasionally does any trace of cellular tissue present itself, in which case the cells are very minute, poly- gonal, and compressed. Mr. J. Quekett has detected calcareous spiculae in the test of this species. They are situated towards the ex- terior, and are very numerous and excessively minute. Their form is usually cylindrical, with triradiate or 4-5-fid extremities.* The composition of the test of Clave/Una lepadiformis cor
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 1196 TUNICATA. mogeneous structure crowded with " nuclei" and bloodvessels, and only occasionally does any trace of cellular tissue present itself, in which case the cells are very minute, poly- gonal, and compressed. Mr. J. Quekett has detected calcareous spiculae in the test of this species. They are situated towards the ex- terior, and are very numerous and excessively minute. Their form is usually cylindrical, with triradiate or 4-5-fid extremities.* The composition of the test of Clave/Una lepadiformis corresponds in all respects to that of the above mentioned Ascidice; certain parts in the same individual having a more particular resemblance to one species, and others to another. The test, however, is quite destitute of bloodvessels. Transverse sections of the stalk of the Clavellina and of the excrescences that spring from it, exhibit a tissue composed of round or elongated non-nucleated cells, O'OI"'—0-014'", almost destitute of inter- mediate tissue, and arranged very close to one another. It is only towards the upper extremity of the stalk that the cells become more and more separate, and even disappear little by little, as happens in some Ascidice, and give place to an intermediate homogeneous substance, bear- ing a quantity of nuclei. In the largest and superior moiety of the test a peculiar structure is found. Externally is a dense, but not thick, layer of delicate cells, which are very difficult to recognise, and measure about O'O^'". Be- tween the cells, and immediately at the surface, are crystals of carbonate of lime, scattered nuclei (measuring G'002"'), and large round fatty granules. Interiorly to this occurs a still thinner lamina, composed of a trans- parent, colourless, homogeneous substance, with infinitely minute pale granules. Next, there is a layer of round granules or vesicles. These are spherical, measuring 0-0005'", 0-0004/&qu
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