394 Rev. T. HIncks on the History of the Hydroida. 



material than the rest. These are tinbranched, and bear at 

 their summit a single polypite. Associated with them are 

 much longer stems, branched for the most part unilaterally, 

 and invested by a polypary exhibiting the curious structure 

 described by Alder. Polypites are borne on the summit of the 

 main stem and of the several ramules. The polypary is com- 

 posed of two layers or coats, distinctly separated from one 

 another — the outer transparent and membranous, the inner of 

 a decided horn-colour and for the most part strongly ringed*. 



Every here and there portions occur in which the separation 

 of the two coats is not apparent ; but throughout the greater 

 part of the stems and branches it is strongly marked. 



The inner tube is completely filled by the coenosarc ; its 

 carinated rings are connected with the epidermis by frequent 

 processes. Towards the base of the stems this singular struc- 

 ture is not generally distinguishable ; but the '^ thin and 

 transparent" polypary, which Allman describes as occurring 

 in his specimens for some distance below the polypite, is no 

 doubt the epidermal layer, forming in other parts of the stem 

 a continuous distinct envelope, and enclosing the annulated 

 tube which immediately surrounds the coenosarc. It appears 

 that the form with short and simple stems, associated in the 

 Firth-of-Forth specimens with the larger branched form, not 

 uncommonly occm*s alone ; and as in this condition it bears 

 the reproductive bodies freely, it cannot be accounted im- 

 mature. 



That the Tuhularia implexa, Alder, and the Firth-of-Forth 

 species are identical is beyond a question f; and Dr. Wright's 

 specimens show that the humbler form described by Alder 

 (as Coryne pelagica) and by Allman, and found by myself at 

 Ilfracombe, is only one state of the same species. A complete 

 diagnosis of Zandea implexa^ therefore, must include the 

 branched double-coated stem, which belongs to the perfect 

 condition of the zoophyte. 



The polypites have five or six large-headed tentacles round 

 the oral extremity; the rest have very small capitula, containing 

 a few thread-cells. I have noticed a large oval thread-cell at 

 the base of most of the tentacles and imbedded in the ectoderm 

 at various points, where tentacles would probably have been 

 developed. Occasionally one occurred in the course of an arm, 

 and a group on the surface of the body. 



The gonophores are borne in large clusters, and number 



* Vide * History of the British Hydroid Zoophytes,' pi. 9. fig. 3 h. 



t I have compared specimens of the polypary of the former, received 

 from Mr. Alder, with the latter ; and they exactly agree, as already ob- 

 served by Wright. 



