McCrady.] 182 [Dec. 3 



throw out from its stem a multitude of long branches without polyp- 

 heads, evidently, according to my interpretation, in consequence of 

 conditions unsuitable to its ordinary mode of sustentation and 

 growth. The long branches thus thrown out seem to be efforts to 

 secure a more suitable location ; and usually, according to my impres- 

 sion, do not appear unless the polyps are in a sickly or dying condi- 

 tion. The fact seems to indicate that the branching stem of the 

 Sertularian is really the persistent embryo, or planula become arbo- 

 rescent. In this state it normally produces by gemmation polyps 

 which remain in sarcocoenonia, if I be permitted the term, with the 

 ramifying embryo; and in Antennularia and Aglaophenia, as Allman 

 has shown, the ramifying embryo also produces in the accessory cel- 

 lules, rhizopodous sarcode extensions of its substance, containing 

 lasso-cells; whence it is easily conceivable that by these alone the 

 embryo might capture and digest its food; while in Hincks' genus 

 Ophiodes, these accessory bodies take on a remarkable development 

 so as to present the form of tentacula, capable of varied movements. 

 Prof. Allmau even advocates the view that the palaeozoic Graptolites 

 are the horny stems of such nematophorous, polypless embryonic 

 forms, and his view is worthy of most attentive consideration. How- 

 ever that may be, the facts forcibly indicate that among the Sertula- 

 rians the branched polyp stem, with its numerous and often annular 

 articulations, is a branched vermiform larva, capable of independent 

 existence under favorable circumstances. And this interpretation is 

 supported by the phenomenon of frustration, which also we owe to 

 Allman, and which is probably the complement of that development 

 of long branches observed by myself in Obelia^ or an allied genus. 

 In this case the coenosarc of the long branch transversely divides it- 

 self spontaneously into small frustules resembling planulse in all re- 

 spects except the want of cilia. 5 These next escape from the rup- 

 tured extremity of the chitinous sheath of the branch, find new places 

 of attachment, and without being themselves metamorphosed, give 

 out buds which develop hydroid polyps at their free extremities. So 

 that the embryo is still capable of multiplying itself by a process 

 peculiar to itself. We may doubt, therefore, whether the stems of 

 the Tubularians are indeed always strictly homologous with those of 

 the Sertularians. They are frequently produced from a polyp al- 

 ready formed; and it is singular that similar frustules observed by All- 

 man in Corymorpha, actually developed directly into polyps, instead 

 of producing the polyp through the medium of a bud. 



