igii.] F. H. Stewart: Development and Anatomy of Cirripedes. 35 



of certain barnacles, while, on the other hand, he established the fact that the large 

 form of the apparently andro-dioecious species was truly and functionally herma- 

 phrodite (5. vulgare). 



In regard to the sexual purity of the apparently male dwarf forms, Darwin (5, 

 p. 289) wrote : '' I was not able to discover a vestige of ova or ovaria in the two male 

 Iblas iquadrivalvis and cumingii) ; and I can venture to affirm positively that the 

 parasites of Scalpellum peronii and villosiim are not female." Hoek also appears to 

 have no doubt as to the purely male characters of these little forms. Gruvel, on the 

 other hand, claims to have found rudimentary female organs in the male of Scalpellum 

 peronii (7, p. 121) . ''Or j'ai rencontré, dans des coupes transversales du pédoncule, 

 quelques cellules arrondies, à noyau assez gros et nucléole très brillant, ne ressem- 

 blent nullement à des cellules cémentaires et que je crois être quelques cellules ovari- 

 ennes non développées, reste, évidemment, de la forme hermaphrodite ancestrale." 

 This is the only species in which he has found cells of this nature. 



Such a discovery would be of very great theoretical importance, since it would 

 suggest that the evolution of the unisexual from the hermaphrodite form occurred 

 gradually by the slow progressive diminution of one set of sexual organs. Such a 

 change would in all probability be due to either (i) a disuse atrophy, the progressive 

 diminution of activity being primary and the diminution in structural development 

 secondary ; or (2) in the present case the semiparasitic habit of the incipient male 

 might have caused it to diminish in size with a consequent diminution in the struc- 

 tural development of the ovaries. (See also G, Smith, 11, p. 35.) 



It therefore appeared desirable that the matter shordd be further investigated, and, 

 in order to arrive at a conclusion as to the nature of the various cells found, it was 

 necessary (i) to trace the development of the ovary in a hermaphrodite or female 

 and thus to become acquainted with the various appearances of the ova in all their 

 successive stages from the earliest point at which they can be recognized ; having 

 done this, to examine the different cells tobe found in the male and its larval stages, 

 and to compare them with the developing ova: (2) to trace the development of the 

 testis in a hermaphrodite and to ascertain if anything similar could be found in a 

 ''female." 



To obtain the best results, it was also clearly desirable to examine males and 

 females, which differed in the least degree possible from the hermaphrodite type 



For this purpose the male of Scalpellum sq uamulif em m, Welt., and the female 

 of Ibla cumingii, Darwin, were chosen. The former differs from its hermaphrodite 

 chiefly in size and in the absence of peduncular plates and latera. The separation of 

 the capitulum from the peduncle is quite as marked as in Scalpellum peronii, and the 

 six chief capitular valves are well developed. The latter, Ibla cumingii, has a close 

 ally in /. quadrivalvis. Darwin (5), in defining the latter species, wrote: "All the 

 external parts (of the hermaphrodite) so closely resemble those of 5. cumingii that 

 it would be superfluous to describe more than the few points of difference " (p. 204). 

 Indeed, the chief point of distinction of the two species lies in the fact that the large 

 form of Scalpellum quadrivalvis is hermaphrodite and possesses a penis, whereas the 



