HINCKS, ON THE POLYZOAN OVICELLS. 279 



lopment of the ciliated embryo and its relation to the ovicell, 

 and which are^ I believe^ conclusive against the marsupial 

 theory. 



I may remark, however, in the first place, that the common 

 opinion could not be correctly represented as a mere " assump- 

 tion," even Avhen Professor Huxley^s paper appeared. For 

 as early as 1845 Professor Reid, in a communication to the 

 ' Annals,' vol. xvi, p. 385 (" Anatomical and Physiological 

 Observations on some Zoophytes "), had recorded the results 

 of his examination of the ovi cells of Flusti'a avicularis and 

 the contained ova, and had clearly pointed out that the latter, 

 in the first stage of their growth, " adhere to the upper end 

 of the lining membrane of the capsule," and are enclosed in 

 a sac formed by a reflection of this membrane. In his 

 account of the structure of the Polyzoa in the ' British 

 Zoophytes,' Dr. Johnston has referred to Professor Reid's in- 

 vestigations, and adopted his views. 



My own observations, repeatedly made on several species, 

 completely agree with Dr. Reid's, and leave no doubt that 

 the ovum, which is ultimately developed into the ciliated 



embryo, is produced within the ovicsll, in an ovarian sac, 

 which buds from the endocyst, at the upper extremity of the 

 capsule. 



I shall briefly detail the various points which have come 

 under my notice, and trace the growth of the capsular ovum 

 from its first appearance to its final exit. 



The species upon which my observations have been made 

 are Bugula flabellata (the Flustra avicularis oi Reid), B. turbi- 

 nata, and Bicellaria ciliata. In all these forms the ectocyst is 

 strengthened by the deposition of calcareous matter. The 

 ovicell is a stony receptacle, lined by an extension of the en- 

 docyst or inner coat, which constitutes the wall of the peri- 

 gastric cavity and encloses the body of the polypide. This 

 lining membrane, according to Dr. Reid, " stretches across 

 the aperture in the capsule." 



The examination of anumber of ovicells enables us to deter- 

 mine the following stages in the development of the ovum. It 

 appears at first as a minute mass of granular substance, in 

 contact with the endocyst, at the top of the capsule, and 

 enclosed by a well-marked sac, formed by a reflection of the 



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