212 ANATOMY OF SPECIAL FORMS. 



(fig. 1 2), about half a line in their longer diameter and one eighth of a line in the shorter. They 

 appeared to be composed of a soft, minutely granular, colourless substance, and their intei'ior was 

 occupied by a very distinct cavity. They were destitute of cilia, and were invested by an extremely 

 delicate membranous or mucous tube, quite structureless, which extended for some distance beyond 

 their ends and adhered for its whole length to the side of the jar. 



Besides these little bodies others (fig. 13), which I do not hesitate to regard as the same bodies 

 in a more advanced stage, were also found attached to the sides of the jar. They consisted of a 

 colourless tubular filament, about four lines in length, attached to the glass by one extremity and 

 developed at the opposite into a minute hydranth, having a general resemblance to the hydranth 

 of Corymorpha, but with only six or eight tentacles in the proximal circlet, while the distal 

 circlet was also composed of six or eight tentacles, which were shorter than the proximal ones, with 

 blunt, almost capitate extremities, and, like the proximal tentacles, disposed in a single verticil. 



Others (fig. 14) representing a still more advanced stage were also found attached to the 

 sides of the jar. They had attained a size about double that of the last, while the posterior 

 tentacles now presented a verticil of sixteen or twenty, and the anterior ones, though still dis- 

 posed in a single verticil, had become multiplied to about the same extent. 



Beyond these three stages I was unable to trace the development through any further steps. 

 The last of them, however, manifestly requires little to convert it into the form of the advdt 

 Corymorpha. 



If it were not that the medusa thrown off from the adult hydroids in my jars had, so far 

 as I could find, all perished before the formation in them of generative elements, I should have 

 regarded the little organisms just described as presenting three stages in the development of the 

 embryo from the ovum. In the absence, however, of all evidence of the presence of ova, we must 

 seek for some other explanation of these little bodies. The phenomena of spontaneous fission, 

 already described as occiu-ring in a campanularian (see above, p. 152, woodcut, fig. 61), will here 

 afford a clue, and the close resemblance of these enigmatical bodies to the fission fmstules of the 

 campanularian will suggest the probability that they represent different stages in the development 

 of fragments which had been spontaneously detached from some of the filamentary processes 

 emitted from the proximal end of the adult specimens in the jar. 



Clavatella prolifera. 

 Plate XVIII. 



Clavafdla prolifera, though of small size, is unrivalled in the elegance of its form, while its 

 wonderful ambulatory medusae present a combination of characters which, if we except the closely 

 allied Elcutheria of De Quatrefages, is quite unparalleled among hydroid planoblasts. 



The Hydrophyton. — In this remarkable little hydroid the hydrocaulus is rudimental, having 

 for its sole representative very short simple processes (fig. 1), which are given off at intervals 

 from a creeping filiform hydrorhiza, and which carry each a hydranth on its summit. These 

 processes as well as the hydrorhiza are invested by a delicate perisarc. 



Tlie Hydranth. — The hydranth is well developed, and when extended is of an elongated, 

 nearly cylindrical form, abruptly dilated at its base and carrying on its distal extremity a single 



