128 Dr. Strethill Wright's Observations on 



nularias and others; the zooid of several elements in the five-lipped 

 polyp of Trichydra (T. S. W,) ; that of many elements in the polyp 

 of Tubularia indivisa, which I have elsewhere shown to be formed 

 by the confluence of the several distinct tubes of which the po- 

 lypary or ccenosarc is composed, each of which tubes may be 

 traced, by its coloured endodermal ridges, to the mouth of the 

 polyp, and bears its own system of tentacles and reproductive 

 apparatus. 



The compound character of the polypary is also seen in Hale- 

 cium and Antennularia, and in a very beautiful manner in the 

 very early state of Sertularia pumila, which (after it had been 

 kept a few days in fresh water) I have figured with the camera 

 in PI. V. fig. 12. Its resemblance to Carus's figure of the Me- 

 dusa, Cunina glohosa (Esch.), which I have copied in fig. 11, is 

 very striking. 



As the Medusa is a multiplex organism, we must inquire how 

 far it is homologous with the generative sac of the Hydroid 

 Zoophyte. 



Prof. Allman, in his paper on Cordylophora (Phil. Trans, vol. 

 cxliii.), advanced the doctrine that the generative sac was homo- 

 logous with the whole Medusa — a doctrine based upon an erro- 

 neous conception of the cavity in which the generative elements 

 are contained. In a " Note on DicEcious Reproduction in Zoo- 

 phytes " (Edin. New Phil. Journ. vol. iv. p. 88), I stated that 

 " the reproductive buds [generative sacs] (of Coryne) were filled 

 with ova developed from the exterior of a hollow central stalk, 

 a diverticulum of the alimentary canal ;" and further, " The 

 peduncle of the Medusa-bud [or budded Medusa] appears to me 

 to be homologous with the entire reproductive capsule [genera- 

 tive sac] (of Coryne glandulosa, &c.)." This view is now adopted 

 by Prof. Allman, who writes, in this Journal (vol. vi. 3 ser. p. 4), 

 " The manubrium is the whole of the * peduncle,' ' stomach,' or 

 by whatever other name it may be called, which depends from the 

 centre of the umbrella in a Medusa or medusoid ; and I apply 

 the same term to what I consider the homologous part in a 

 sporosac, namely the whole sporosac mintis the ectotheca and 

 mesotheca." Now, the 'sporosac,' less the 'ectotheca' and 

 ' mesotheca,' is the simple generative sac, which therefore Prof. 

 Allman has agreed with me in considering homologous with the 

 peduncle. 



But I would now very much modify the above view. We 

 must keep in mind that each of the eight elements of a medusoid 

 has three distinct functional subelements ; that the single repro- 

 ductive subelement of the Medusa exists, as in Stomobrachium, 

 uncombined ; that where the peduncle is the reproductive organ 

 of a free Medusa, as in Sarsia, it consists of two subelements 



