132 THE CRUSTACEA 



off on the inside the absorptive roots which, in the case of Sacculina, 

 penetrate into all the organs of the host, with exception of the gills 

 and the heart, and extend to the terminal segments of the legs and 

 into the antennules and eye-stalks. The roots are covered by a 

 very delicate cuticle, beneath which is a layer of hypodermic cells, 

 and the interior is occupied by reticular connective tissue, only the 

 larger trunks having a central cavity. At the tips of the rootlets 

 in Sacculina the outer layers are invaginated to form a cavity known 

 as the "lagena." In the genus Duplorbis, where the root-system 

 appears to be absent, the peduncle is hollow, its cavity communicat- 

 ing with the closed mantle-cavity and opening at the other end into 

 the body-cavity (haemocoel) of the host. 



Internal Anatomy. Apart from a single nervous ganglion (Fig. 

 80, B, g) which lies close to the mesentery near the female genital 

 openings, the only organs present are those of the generative 

 system. The ovary (ovy) is divided into two much-lobed masses 

 united by a median portion and giving off on each side a short 

 oviduct, which widens into a " genital atrium " (at) before opening 

 into the mantle-cavity. The walls of this atrium, as in the normal 

 Cirripedes, are glandular, often growing out into branched tubular 

 glands (yl) ("colleteric" glands) supplying the material of the 

 envelopes within which the eggs are packed in the mantle-cavity. 

 In Sacculina the egg-masses are retained in position by barbed 

 spines (" retinacula ") grouped on papillae on the lining membrane 

 of the mantle. 



The testes (t) have each the form of an elongated sac narrowing 

 towards a short vas deferens. The spermatozoa are filiform and 

 actively motile. 



F. Miiller was the first to suggest that the Cypris larvae, which, 

 as Lilljeborg had previously observed, are often found attached 

 near the mantle-opening of young specimens of Peltogaster, might be 

 complemental males. Delage accepted this interpretation for the 

 larvae which he observed in the same position in Sacculina, but he 

 was unable to obtain them alive or to observe any trace of male 

 organs. At this stage the mantle-opening is still closed by a plug 

 of chitin, and it is difficult to see how fertilisation could be effected. 

 G. Smith, who has recently investigated the subject, finds that the 

 larvae die very soon after they become attached, without developing 

 further. In only one instance did he find evidence of what seemed 

 to be an abortive attempt of the cellular contents of the larva to 

 pass into the tissues of the mantle in the way in which the contents 

 of the larvae pass into the host in the ordinary course of develop- 

 ment. G. Smith believes the attachment of these larvae to be an 

 atavistic phenomenon ; that the larvae are, in fact, vestigial male 

 individuals. The same observer has found in the mantle-cavity of 



