39. 



ovarian cells in the Ventriculidse lie imbedded in the substance 

 of the polypidom, replacing, where they occur, the substance of 

 the central polypidom, but entirely inclosed, on each surface, by 

 the polyp-skin (PL VIII. fig. 3.) Their character is the same in all 

 varieties. No polyps or processes exist on that part of the polyp- 

 skin which overlies them. It is perhaps riot unworthy to be 

 noticed that there are generally found, on specimens having no 

 ovarian cells, small patches, of the same shape and scattered in 

 the same way over the surface as the ovarian cells, in which there 

 are no polyp-cells. The suggestion naturally occurs, whether 

 these are the spots in which, at the proper season, ova would 

 be developed ? The under-skin is entire in these places. 



Sufficient it is hoped has been adduced to show that the Ven- 

 triculida3 must have been zoophytes of a very high order* ; that, 

 in point of fact, characters are found in them which belong only 

 to the higher among the Polyzoa or Ascidian polyps ; and that 

 those characters belong to different groups among those Ascidian 

 polyps. It has been seen that the moveable processes found in 

 some recent Escharidaj and a few other forms were combined with 

 some important characters found principally marked in the recent 

 Halodactylus ; and it is not unimportant to remark, that the Halo- 

 dactylus is superior to most other recent Polyzoa in not being a 

 mere aggregation of distinct cells, but in having a distinct cen- 

 tral polypidom f, other than the membrane containing its imme- 

 diate polyp-cells, and other than the remains of dead polyp-cells. 

 The central polypidom of the Halodactylus is composed of 

 a network, very irregular however, which the polyps surround 

 on all sides. In this it approaches the Ventriculidse, but the 

 latter far exceeded it in the perfection of all parts of that poly- 

 pidom, as they obviously did also in firmness % as well as in regu- 



analogy between the embryology of the Ventriculidse and that of many 

 recent zoophytes, but I have not embodied them above, fearing that it 

 would tend to complicate the subject and distract attention from the con- 

 nected argument which I have endeavoured to set forth demonstrative of the 

 affinities of the Ventriculidae. 



* I use the language here of those who include Eschara and Flustra 

 among zoophytes. If they were true Ascidians, the Ventriculidas were true 

 Ascidians also, only more highly developed. 



t This also marks Tubulipora patina very beautifully, whose general 

 likeness to many Ventriculidae has been already noticed. I have found a 

 remarkably fine specimen in the London clay of a polypifer, folded up after 

 the manner of Eschara foliacea, but with a distinct and very regularly con- 

 structed central polypidom. The species (? genus) is undescribed. My spe- 

 cimen is five inches square and four inches in thickness. 



J It will occur to the reader that the security of Eschara, Flustra, &c. was 

 ensured either by their parasitic growth or the calcareous nature of their 

 polypidom. The Ventriculite, having neither of those characters, had the 

 special provisions exhibited in its polypidom to secure, still more perfectly, 

 the same objects, while the separate and peculiar nature of its root gave to 

 its polypiferous surface a wider range and sphere than either EscJiara or 



