360 Dr. T. S. Wright on the Reproductive Elements 



XLI. — On the Reproductive Elements of the Rhizopoda. 

 By T. Strethill Wright_, M.D. 



[Plate XVIII,] 



We have, as far as I am aware, no definite observations as to 

 the reproductive elements of the Rhizopods. All who are accus- 

 tomed to the observation of minute marine life know that these 

 creatures increase with great rapidity ; but how they increase is 

 at present a mystery. 



Prof. Carpenter* has recorded and figured a peculiar state of 

 the sarcode as occurring in spirit specimens of Orbitolite, which 

 appeared to be broken up into little spherules, though still re- 

 taining the structure of unchanged sarcode. He also states that 

 similar spherules are figured by Ehrenberg in several of the cells 

 of Sorites orbiculus, and by Schultze in the chambers of Rotalia. 

 Dr. Carpenter is inclined to believe that these bodies are gem- 

 mules. 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 object, found in an imper- 

 fectly 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 fol- 

 lowing observations. 



With regard to the female element, it will be necessary first 

 to ascertain the essential characters of an ovum. Prof. Allan 

 Thompson t defines it as " a detached spheroidal mass of organ- 

 ized substance, of variable size, enclosed in a vesicular mem- 

 brane, and containing, in the earlier periods of its existence, an 

 internal cell or nucleus." But the presence 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 can- 

 not 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 defi- 

 nition which will apply also to the fii'st stage of the ovum of 

 Rhizostoma as figured by Prof. Thompson J, where he shows, 

 first, the '* primitive ovum " destitute of germinal vesicle and 



♦ Phil. Trans, vol. cxlvi. p. 212. 



t Cyclopaedia of Anat. and Phys. vol. v. p. 128. 



X Op. cit. p. 128. 



