OF POLYPES. 47 



Htion of the fleshy central part of "the stem,) are enclosed in ve- 

 sicles of the same texture as the polypidom itself, and neither 

 proceed from, nor have any immediate connection with, the 

 proper body of the polype, being evolutions from the pith or 

 fleshy axis which connects the polypes together, and binds the 

 various heads into one whole. — Such is a brief summary of the 

 facts ascertained on this head, but it behoves me to mention 

 that it is, to a certain extent, at variance with the opinions of 

 Professor Grant. He maintains from his numerous observa- 

 tions on a great variety of zoophytes, that the gemmules by 

 which these animals propagate are highly organized portions of 

 the gelatinous substance of the parent, formed " in almost every 

 known zoophyte," and not merely in the Hydrazoa, as we have 

 limited it, " by the common connecting substance of the ani- 

 mal, and not by the polypi, which appear to be only the mouths 

 or organs of digestion. In Plumularia?, Sertulariae, Campanu- 

 lariae, horny Cellarite, Antennulariae, the ova are formed in ve- 

 sicles which originate from the centre of the stem. In Flustra?, 

 calcareous Celiarise, and some others, the ova are formed in the 

 cells, but exterior to the bodies of the poh/pi, which disappear 

 before the ova arrive at maturity. In the Lobidarise, Gorgonise, 

 Spongiae, Clione, &c. the ova are formed and matured in the 

 common Jleshy substance of the body before they advance to be 

 discharged through the polypi, or the fecal orifices."* 



I'he oemmules exhibit considerable variety in colour, — they 

 are milk-white, yellow, red, pink or green, but sometimes the 

 colour is not fully developed until near maturity. In all the as- 

 cidian polypes they are globular or have a tendency to that form, 

 and appear to preserve it until after their discharge from the 

 body ; but in the Hydroida this is not the case, for although 

 spherical in their earlier stages, " their shape alters on approach- 

 ing maturity ; it elongates, becomes elliptical, next prismatic, 

 and at length each corpusculum issues as a perfect animal from 

 the orifice of the vesicle," and exhibits in figure and in motion 

 much resemblance to the little leech-like Planaria?. (Fig. 6.-}-) 



' Edin. Journ. of Science, No. 14. 



t The figures represent the gemmules of Plumularia pluma. For the draw- 

 ing I am indebted to my friend Dr Coldstream of Leith. 



