208 Mr Harmer, On Gyclostomatous Polyzoa. [Oct. 26, 



with tarsal and metatarsal bones still free, with a quadrate bone 

 not yet fixed, without upper and lateral separate temporal-parietal 

 fossae, with a bifurcated pubis, with a complete alveolar dentition, 

 — but would we call such creatures Dinosaurs, and if so, where are 

 they ? 



(3) Notes on Gyclostomatous Polyzoa. By S. F. Harmer, M.A., 

 King's College. 



(Received Nov. 5, 1896.) 



On a former occasion I announced to this Society the occur- 

 rence of embryonic fission as a normal feature in the development 

 of Grisia 1 . Since that time I have accumulated fresh evidence 2 

 tending to show that the process then described is, with various 

 modifications, characteristic of the Cyclostomata in general. My 

 most recent observations, on Idmonea serpens, L., although by no 

 means completed, have led to results which appear to me not 

 unworthy of the acceptance of the Society. 



The ovicell of /. serpens belongs to a type which is, in many 

 respects, intermediate between that of Grisia and that of Licheno- 

 pora. The colony grows as a lobed encrustation on other objects, 

 and each lobe usually develops an ovicell, which in its fully- 

 developed form appears as a punctate calcareous film extending 

 between the bases of the more distal zooecia. The tubular aperture 

 does not develop until the ovicell has reached an advanced stage 

 of development. The morphology of this type of ovicell has not 

 hitherto been sufficiently studied. 



As in the case of Grisia and of Lichenopora the ovicell begins to 

 develop before it can be recognized externally, since it is at first 

 in no way distinguishable from a zooecium. There can in fact be 

 little doubt that the entire ovicell is a much modified zooecium, 

 its tubular aperture corresponding with the orifice of an ordinary 

 zooecium. 



Sections through the growing edges of vigorous colonies, in the 

 breeding season, commonly reveal the presence of egg-cells in 

 connexion with the caecum of the stomach of many of the younger 

 polypides and buds. These eggs are precisely similar to those 

 which I have observed in other Cyclostomes, or to those which 

 had previously been described, by Claparede 3 , for instance, in the 

 young buds of Bugula. One, two or three eggs are present in 

 each fertile polypide, and each is enclosed in a distinct follicle. 

 The eggs appear in the very young polypide-buds, and in all cases 

 observed, those which are in connexion with the younger polypides 

 show no trace of nuclear division. In the eggs of recently mature 



1 Proc. Cambridge Phil. Soc. vii. 1892, p. 48 [read Feb. 10, 1890]. 



2 Quart. J. Micr. Sci. xxxiv. 1893, p. 199; xxxix. Part i. 1896, p. 71. 



3 Zeitsch. f. iviss. Zool. xxi. 1871, p. 166. 



