xlii THE VOYAGE OF H.M.S. CHALLENGEE. 



partly homogeneous nucleL Most recent investigators, Biitschli in particular (1882, L. N. 41), have 

 pointed out and rightly criticised this confusion. The criticism might, however, have been more 

 justly expressed by stating that, in the preparation of my Monograph (1859—1862), I did not make 

 use of modern methods of demonstrating the nucleus by staining fluids, which were quite unknown 

 at the time, and only discovered a decade later. In fact, without the aid of such reagents, it is 

 quite impossible to distinguish between the various " spherical transj^arent vesicles," of which those 

 found in the central capsule of the Ph^eodaria and many monozootic Collodaria are simple 

 vacuoles lying in the endoplasm, whilst, on the other hand, those of the Polycyttaria and many 

 other Eadiolaria are true homogeneous nuclei. For not only are the general appearance of the 

 small clear spheres, their refractive power, and regular distribution in the endoplasm quite similar, 

 but they are also of much the same size, for the diameter ranges from O'OOo to 0'015 mm., being 

 generally between 0008 and 0"012 mm. In addition to this there is generally in each hyaline 

 sphere a dark brightly shining granule, which, in the case of the vacuole, is simply a fat-granule, 

 whilst in the case of the nucleus, it is a true nucleolus. The small hyaline spheres in the young 

 uninucleate capsules of the Polycyttaria are simple vacuoles (PI. 3, fig. 12), whilst in the ripe 

 multinucleate capsules they are true nuclei (PI. 3, figs 3, 8, 9), and it is quite impossible to discrimi- 

 nate between these two conditions without the use of reagents. This has been expressly recognised 

 by E. Hertwig, who has the merit of having been the first to clearly distinguish, by the aid of 

 staining fluids, between these two different constituents (1879, L. N. 33, p. 108). 



B. The " alhumen spheres" which were first observed by A. Schneider in 1858 in the common 

 cosmopolitan Tlialassicolla nudcata (L. N. 13, p. 40), and which appear to occur in only a few other 

 ThalassicoUida, are distinguished from the ordinary hyaline spheres of about the same size by their 

 higher refractive power and by certain albuminoid reactions, especially the coagulation of a 

 membranous envelope under the influence of certain reagents (see my Monograph, p. 250, and 

 Hertwig, L. N. 26, 1876, p. 46). They often enclose various formed contents, and require further 

 investigation. 



C. The gelatinous spheres of various sizes, found in the endoplasm of the Eadiolaria, agree in 

 their reactions (especially in staining by certain reagents) with the common extracapsular jelly of the 

 calymma, and are hence disting-uishable both from the true (coagulable) "albumen sphere," and from 

 the ordinary watery vacuoles. 



D. The alveoles, which are only accurately known in the case of certain large monozootic 

 Collodaria, but which also seem to occur in the central capsule of other remarkably large 

 Eadiolaria, were described in my Monograph in the case of Thalassolampc ma^'garodes and 

 Physcnvxtium 7nulleri, under the name "intracapsular alveolar cells" (1862, pp. 77, 254, 257). They 

 are not, however, true nucleated cells, and the body described as a nucleus is not such in reality. 

 Nevertheless these large hyahne spheres do possess a special envelope, as I have recently convinced 

 myself by the examination of ruptured central capsules of Thalassolampc maxima, Thalassopila 

 cladococcus, and Physematium atlanticaim (PL 1, figs 2, 3). The central capsule of these 

 Collodaria becomes distended to most unusual dimensions (2 to 12 mm. in diameter) by the great 

 development of these large hyaline vesicles, each of which measures from 01 to 0'5 mm. in diameter. 



73. The Intracapsular Fat-Globules. — Fat is present in the central capsule of all 

 Eadiolaria in larger or smaller quantities, and generally appears in the form of very 



