CR USTA CE A HERMAPHRODITISM 



381 



XII. Hermaphroditism in the Crustacea. 



Hermaphroditism is a rare phenomenon in the Crustacea, and only found in 

 attached and parasitic forms, viz. in the attached and parasitic Cirripedia and 

 in parasitic Isopoda. 1 The sexual relations in these groups are very interesting and 

 must be further briefly described. 



The commoner Balanidce and Lepadidce are hermaphrodite. There are, however, 

 Lepadidce (Ibla and many species of Scalpella) in which, besides the hermaphrodite 

 individuals, dwarf males occur. These latter live parasitically on the bodies of 

 the hermaphrodite individuals, generally in a fold of the mantle at the closing edge 

 of the scutum. In their structure and form they are nowise like the hermaphrodites. 

 They do not advance beyond the so-called Cypris stage, their body is almost vermiform 

 and possesses besides the antennae only 4 pairs of reduced tendril-like feet. The 

 oral limbs are wanting. A mouth is wanting, the enteric canal is rudimentary, 

 and the testes unpaired. It is evident that these reduced dwarf males provide 

 occasionally for the cross fertilisation of the hermaphrodite individuals. 



There are again some species of Scalpella (Sc. ornatum, regium, parallelo- 

 gramma, nymphocola], and further the genera Cnjptophialus and Alcippe, in which 

 dwarf males occur, but in which the individuals which correspond with the herma- 

 phrodite individuals of the related Cirripedia are not hermaphro- 

 dite, but only female. Here, therefore, separation of the sexes 

 prevails with marked dimorphism. The majority of the Cirri- 

 pedia, however, seem to be hermaphrodite without dwarf males. 

 The Rhizocephala are hermaphrodite with dwarf males, which 

 remain at the Cypris stage. 



The hermaphroditism of certain parasitic Isopoda is of another 

 sort. The Cymothoidea are protandrously hermaphrodite, i.e. 

 in youth they are male, later, the male copulatory segments 

 are lost and the adult animals are exclusively female (Fig. 256). 



The sexual relations in the Entoniscidce (Portunion] are pro- 

 bably the following. These large, characteristically-deformed 

 parasites (Fig. 253) are protandrously hermaphrodite, but there 

 are, besides, small males (Fig. 254, A] which have remained in 

 a larval stage, and besides these again other degenerate so-called 

 complementary males. Out of several larvae which reach the 

 host, those which have the best place on its body and are best 

 nourished probably develop into adults which function as females, 

 the second-best nourished larvae remain as males in a larval 

 stage, and all the others become degenerate complementary 

 males. 



The Bopyridse, which are parasitic in the branchial cavity 

 of the Carididce, are sexually separate and strongly dimorphic ; 

 the dwarf males live on the bodies of the females. 



The origin of all these peculiar sexual relations is still very 

 uncertain. Most free living Crustacea are sexually separate, and 

 so are also the free living forms related to the hermaphrodite 

 Crustacea. 



FIG. 256. Herma- 

 phrodite sexual ap- 

 paratus of a young 

 Cymothoa cestroides 

 (after P. Mayer), 

 somewhat diagram- 

 matic, t, Testes ; ov, 



From this, and from the fact that hermaphrodites ovary ; od > oviduct ; 



e -. ,, jjjjLtj^ v ' vas deferens : p. 



are found among the parasitic and attached Crustacea, we may, penis 



with some probability, conclude that hermaphroditism in the 



Cirripedia and Isopoda is an acquired condition, perhaps brought about by the small 



1 The Apusidoe (Phijllopoda] have also lately been shown to be hermaphrodites, 

 with the occasional presence of males. 



