3. On the Hermaphroditism of Fixed Animals. 103 



is a transverse section through an adolescent parasite in the region of the posterior pair of 

 spermathecae. The openings (op) of the latter can be seen protected by the chitinous 

 armature (ch), while dorsally the receptacles of the spermathecae (sp. th) are seen with groups 

 of spermatozoa in them. A high power drawing (fig. 29 a) of these spermatozoa reveals their 

 complete identity with the spermatozoa found in the testes of the Cryptoniscus larvae (fig. 24 a). 



Such is the history of the reproductive processes in Danalia curvata, a history which 

 brings these forms into complete agreement with the rest of the Epicarida, and also with 

 such Isopods as Anilocra etc. whose protandric hermaphroditism has been proved by 

 P. Mayer (2). 



Professor Caullery has drawn my attention to a paper by Mesnil and himself (7) in 

 which the life history of Hemioniscus balavi, parasitic on Balanus balanoides, is very fully 

 described. The hermaphroditism of this animal agrees perfectly with the description we have 

 just given for Danalia. The authors describe the formation of a peculiar brood-pouch in 

 the adult female, which, if it occurs in the Liriopsidae, has been missed by myself and previous 

 observers. 



3. On the Hermaphroditism of Fixed Animals. 



A survey of all living beings will disclose to us that the state of hermaphroditism 

 is closely correlated with a fixed habit of life. In the vegetable world fixation is the rule 

 and hermaphroditism is by far the commonest condition, but it is in the animal kingdom 

 that the special proofs of this contention are forthcoming. For if we consider the special 

 groups which belong to free-living orders of creatures but have themselves adopted a fixed 

 habit, we perceive at once that all these groups exhibit hermaphroditism to a very great 

 extent To take a few instances, the Cirripedes among Entomostraca, the Epicarida and 

 Cymothoidae among Isopoda, and the Ascidians among Chordata may be mentioned. There 

 is plainly then some causal connection between hermaphroditism and a fixed habit; but what 

 is this connection? The most obvious answer to this question is that an animal which is 

 fixed in one place and cannot meet with other individuals of its species can only fertilize 

 itself and hence it has had to develope both ova and spermatozoa. But this answer must 

 certainly be rejected, because wherever hermaphroditism is found the most elaborate means 

 are almost invariably present for ensuring cross-fertilization, either by means of special males 

 or else by the wide -spread occurrence of protandry, while among plants the adaptations for 

 securing cross-fertilization are so remarkable as to need no comment. It is true that in many 

 plants and in a few animals self-fertilization or autogamy does occur normally, but these cases 

 are so few in comparison to the elaborate devices for securing cross-fertilization that it is 

 necessary to regard these cases as something special and not as constituting the normal con- 



