REPRODUCTION OF RHIZOPODA. 39 



protoplasmic mass, is a question as to which there is not at present the sHghtest evidence on 

 either side ; and it is much to be desired that observers who have facihties for the study of 

 the reproduction of the Formmni/era should systematically and perseveringly investigate it. 

 The only observations yet recorded, that indicate the existence of a sexual process in Forami- 

 nifera, are those of Dr. T. Strethill Wright (cxii), who states that on examining a great 

 number of specimens of Gromio, ('ornuspira, Miliola, BoMia, and Orhuliiiu, he has repeatedly 

 discovered bodies which correspond to the " primitive ovum " of ^c«/(^//(«. They consist of 

 transparent spheres or ovoids, formed of a finely molecular substance, in which, however, the 

 molecules are masked or rendered indistinct by the highly refractive matter in which they 

 are imbedded. He was never able to detect either germinal vesicle or germinal spot in the 

 living specimens ; but in a specimen of Trunratuhva which had been hardened in spirit, 

 decalcified by dilute nitric acid, and then mounted with strong heat in Canada balsam (PI. IV, 

 fig. 5), four of the segments (r, c, c, c) each contain an ovum, which shows a germinal 

 vesicle and spot with the utmost distinctness, whilst the rest («/, d) present the usual 

 appearance of granular, low-refracting sarcodc. The ova of Gromia are small enough to 

 escape by the aperture of the "test;"' and as young Groiuia: are met with slightly larger than 

 these ova, it seems probable that the ovum is at once transformed into the body of the ofi^spring, 

 and that it directly acquires an envelope. But in Orhulina and Trtmcattdina the ova are of 

 much larger proportionate size, having in the latter case as much as ten times the diameter of 

 the primitive segment, and being far too large to escape by the aperture of the chambers 

 which contain them. Hence it is considered probable by Dr. Wright that the ova of these 

 genera undergo a polymorphic development of many months' duration, similar to that supposed 

 by Carter to occur in Amwha verrucosa (^ 47) ; and that each ovum becomes transformed by 

 fission (of which process he detected indications) into numerous amoeboid zooids, which escape 

 through the openings of the shell and form the primordial segments of future Rhizopods. The 

 observations of Prof. Schultze upon Rolalia, however, would rather lead to the inference 

 that the segments into winch the ovum breaks up remain in connexion with each other, and 

 constitute, not the primordial segment only, but the segments immediately succeeding it, in 

 each of the young, and that these escape by the rupture of the shell of the parent. — Specimens 

 occasionally present themselves which indicate that a partial binary fission of the germ may 

 take place at a period anterior to the calcification of the wall of the primordial segment. 

 Thus Prof. Williamson (ex) has described a twin monstrosity of Entosolenia (fig. 32, a), and 

 a similar example of Z)«^/«//«« (fig. 49), which have obviously originated in an incomplete 

 subdivision of the primordial segment ; and he states (p. xi) that " whenever such specimens 

 occur, it invariably happens that the two halves of the twin organism belong to the same 

 variety or type," — a fact of some importance as indicating that the transmission of varieties 

 is eS"ected, as in Plants, by those processes of subdivision which take place under the form of 

 fission or gemmation, whilst the origination of varieties is rather to be looked for in sexual 

 generation. Some curious examples of the same kind of " monstrosity by excess," occurring 

 in Orbitolitefi, have been described and figured by myself (xiii) ; and in those cases also. 

 Prof. WiUiamson's general statement was fully borne out. 



