112 



MORPHOLOGY. 



Fig. 48. 



FihriUated tmite. — In a great many cases there is developed upon tlie inner surface of tiie 

 ectoderm a peculiar tissue, forming an abrupt Ijoundary between the ectoderm and endoderm. 

 It may be well seen in those elongated hydranths which present an extensive surface uncovered by 

 the more or less opaque chitinous perisarc, such as Clava, Ili/drac- 

 tinia, and Clavatella, and in the very contractile body and tenta- 

 cles of the hydranths of different CorynidcB, and in the stem and 

 hydranth of Corymorplia. In all these cases it presents the appear- 

 ance of fine, close, longitudinal and parallel strise between the ecto- 

 derm and endoderm. From the body of the hydranth these stripe 

 usually extend into the tentacles, and may be very distinctly seen 

 in the tentacles of Coryne pusilla, where they can be easily traced 

 as far as the terminal capitulum. 



I have succeeded in isolating the fibrillated tissue of the large 

 tentacles in specimens of Tiibularia indimsa, which had been kept 

 some years in spirits. The fibrillated tissue here (PI. XXIII, fig. .5) 

 consists of two layers, one composed of filu'es which take a 

 longitudinal course parallel to the axis of the tentacle, and the other 

 of fibres which take a circular course transverse to the axis. The 

 circular fibres seem to lie externally to the longitudinal, and both 

 form a muscular envelope which is intimately connected with the 

 ectoderm of the tentacle, and comes away with the latter when this 

 is separated from the endoderm.' 



The fibres thus isolated appear to be tubular, having a dia- 

 meter of about 5Tfg^ of an inch ; they are perfectly smooth, but in 

 most cases a very distinct oval nucleus, having a greater diameter 

 of about -25770 of an inch, and with a brilliant nucleolus, may be 

 demonstrated in them. Tliey may sometimes be seen to taper away at each end to a point, when 

 they present the appearance of greatly elongated fusiform cells (fig. 6). 



That the fibres thus demonstrated in the Hydroida constitute a true contractile tissue would 

 follow, not only from the analogy suggested by structure, but from the fact of contractility mani- 

 festing itself with great intensity in those parts where they are best developed.^ 



Part of a tentacle of Syncoryne 

 ^M^c//e//«, showings the superficial 

 protoplasmic layer. 



a. Large-celled tissne of endo- 

 derm, forming the axis of the ten- 

 tacle.the cells containing nncleated, 

 and often radiating, masses of pro- 

 toplasm; i, fibrillated layer; c, 

 ectoderm, with immersed thread- 

 cells ; d, superficial layer of proto- 

 plasm, which has become extended 

 here and there into e, e, e, filaments 

 of extreme tenuity. 



' lu some cases the fibrillated tissue would seem to be more intimately united to the endoderm 

 than to the ectoderm. I have found, at least, that in specimens of C/ava squamata, which had been 

 preserved in spirits, the ectoderm could be detached, leaving the fibrillated layer still adlierent to the 

 endoderm. 



^ Reichert (" Ueber die contractile Substanz und den feineren Bau der Campanularien," &c., 

 ' Monatsbericht der Akad. der Wissens. zu Berliu,' July, 1866, p. 504) denies the existence of the con- 

 tractile fibrillated layer whose presence is here insisted on, and maintains that its place is taken by a 

 structureless membrane, to which he gives the name of supporting lamella (" Stiitzlamelle"), and 

 which he regards as a sort of internal skeleton secreted from the inner side of the ectoderm. He 

 believes that the whole contractility of the hydroid resides in the ectoderm itself, which he says is 

 entirely destitute of cells or cell-constituents. My own observations will not allow me to adopt the 

 views of Reichert. 



