Observations on British Zoophytes and Frotozoa. 271 



state of the sarcode as occurring in spirit specimens of Orbi- 

 tolite, which appeared to be broken up into little spherules, 

 though still retaining the structure of unchanged sarcode. 

 He also states that similar spherules are figured by Ehren- 

 berg in several of the cells of Sorites orbiculus, and by 

 Sehultze in the chambers of Botalia. Dr Carpenter is in- 

 clined to believe that these bodies are gemmules. I have 

 repeatedly noticed bodies, apparently similar to those figured 

 by Carpenter, in Gromia ; but I have considered them to be 

 of the same nature as the coloured spherules which are found 

 within the endoderm of the Hydroid Zoophytes. 



Besides these spherules, however, Dr Carpenter has met 

 with other bodies, apparently imbedded in the sarcode, which 

 he considered might be gemmules in a later stage, or ova. 

 These were of a deep-red colour, and exhibited various 

 stages of binary division. He has also figured a third ob- 

 ject, found in an imperfectly closed shell of Orbitolite, which, 

 with his usual caution, he considered might possibly have 

 been introduced from without. 



It is under these circumstances that I bring forward the 

 following observations. 



With regard to the female element, it will be necessary 

 first to ascertain the essential characters of an ovum. Pro- 

 fessor Allan Thomson* defines it as " a detached spheroidal 

 mass of organised substance, of variable size, enclosed in a 

 vesicular membrane, and containing, in the earlier periods 

 of its existence, an internal cell or nucleus." But the pre- 

 sence of a nucleus is not essential to the constitution of an 

 ovum ; for in the ova of Chrysaora hyoscella and some of the 

 Ctenophora (Beroe) it cannot be detected at any stage. 

 The ova of these animals may be defined as " detached 

 masses of highly refractive substance." Such appears to be 

 the simplest definition of an ovum — a definition which will 

 apply also to the first stage of the ovum of Bhizostoma as 

 figured by Professor Thomson, f where he shows, first, the 

 " primitive ovum" destitute of germinal vesicle and spot ; 

 secondly, the appearance of the germinal vesicle ; thirdly, 



* Cyclopaedia of Anat. and Phys., vol. v. p. 128. 

 t Op. Cit. p. 128. 



