224 ZOOPHYTES. 



Plate XII. Fig. 9. Sertularia si/ringa investing both sides of a section of the 

 Sertularia dichofoma. 

 10. Hydra and empty cells of another specimen. 

 Both figures are enlarged. 



§ 5. Sertularia arcta — The Crowded Sertularia. — Pl. XLII. 

 — Much hesitation may be entertained regarding the correct position 

 of this product, which is apparently allied to some inteimediate genus 

 approaching the investing Fhistrce. But the Ascidian hydra of the Flustra 

 itself, denies its reception there : neither, for the same reason, can it be 

 confounded with the AlcyonidicB, to which, in perfection, it bears some 

 analogy ; for here the zoophyte is hydraoidal. Leaving its precise place, 

 for the present, the product is now introduced merely for the convenience 

 of associating it with other hydraoids. 



It is generally found as a small, irregular, flattened mass, seldom of 

 regular figure, seated as a parasite on the angles formed by uniting 

 branches of the Sertularia falcata. The dimensions and the shape are 

 alike various. Sometimes it is six lines by two, if of an oval figure. — 

 PI. XLII. fig. 1 ; but rarely appearing so symmetrical. — Fig. 2. 



In as far as I have yet observed, this mass consists of a single stratum 

 of long, curving, tubular cells, crowded closely together. — Figs. 3, 4. 

 Where best exposed, as on the margin, the curvature is most conspicuous, 

 that of some, there exceeding a semicircle. — Fig. 4. 



A hydra with eight muricate tentacula occupies each cell, stretching 

 much beyond its circular orifice, but offering nothing else remarkable. 

 The complement of tentacula may be rated at eight, though some indivi- 

 dual hydriTc have ten. 



This product is not common ; it has never occurred to me otherwise 

 than as a parasite ; and it may be readily overlooked. 



Propagation. — Here, as in many preceding species, the perpetuation 

 of the species is effected through the medium of a planula, such as is pecu- 

 liar^ under some modification, to that which is the origin of zoophytes, 

 whose hydrse are provided with muricate tentacula. This animal appears 



