HISTORY OF RESEARCH. lxiii 



Hall; the "funiele" is regarded as being composed of the proximal extensions 

 of the axis, together with, probably, the common canal. The distal extension of 

 the axis is only seen in Diplogrcvpsus. It may consist of the solid axis only, or of a 

 "bladder-like body, more or less elliptical in form, with a distinct filiform margin, 

 and of uncertain function." "This dilatation," as seen in the new species l>. vesi- 

 culosus, "seems always to be a direct expansion of the axis, which would thus 

 appear to be tubular." 



The non-solid character of the axis, at any rate in some forms, though hinted 

 at by previous authors (Suess, etc.), was thus definitely stated by Nicholson for 

 the first time. As regards the homologies of this axis, Nicholson thinks it is 

 "probably related (but by analogy only) to the horny or calcareous ' sclerobasis ' of 

 the Gorgonidae and Pennatulidae." Its chief function was to give support, and 

 its radicle was not used for purposes of attachment; therefore there is no close 

 parallel between it and the foot stalk of the Sertularidae. 



Tlir common canal. — He considers that the common canal is an individual 

 structure, "giving origin to the cellules" and conveying a "soft connecting 

 substance uniting the various polypites into an organic whole." He considers it to 

 be homologous with the coenosarcal canal of zoophytes generally. 



Cellules. — Nothing new is added by Nicholson in this paper concerning the 

 structure of the cellules. He points out their resemblance to the hydrothecae 

 of the Sertnlaridfe, but is opposed to the view that they were cut off from the 

 common canal by a diaphragm. 



As regards the development of the Graptolites, Nicholson inclines to the opinion 

 that the "germs" at present discovered are not the earliest forms of the embryo; 

 these probably had no corneous test. He agrees by implication with Barrande's 

 view that the youngest cells are at the proximal end of the polypary, and in 

 consonance with this he expresses the opinion that the secondary cellules appear 

 to be intercalated betAveen the radicle and the primordial cellules, so that the 

 youngest cellules are proximal, the oldest distal in position. This mode of develop- 

 ment "corresponds with that observed in the Calycophorida3 and Physophoridae." 



Nicholson's previously published views on the reproductive organs of the Grapto- 

 lites are summarised in this paper. He thinks that when the capsules dropped off, 

 probably minute, ciliated, free-swimming organisms (? planula?) were liberated, 

 which, at a later stage, developed a corneous covering. He suggests that the 

 vesicle of D. vesiculosus (which was here figured for the first time) was in some 

 way connected with the process of reproduction. 



As to the mode of existence of the Graptolites, Nicholson says "there can he 

 no question that by far the greater number were free-swimming or free-floating 

 organisms." Some had floats; others were very probably provided with 

 " necto-calyces," or swimming-bells, but these would not be preserved. The 

 Dendroid forms, which most closely resemble the Sertularidae, may have been fixed, 



