98 MICROSCOPICAL STUDIES. 



twining around the viscera and insinuated among the caeca of the 

 liver. Nutrient matter is there obtained and is thence conveyed to 

 the sac-like body. The latter contains neither alimentary canal, 

 limbs, or other appendages. Shortly stated, its structure is that of 

 a double walled sac, the inner of which contains large lobate ovaries, 

 closely united, 2 testes, 2 cement glands, and a single nerve ganglion. 

 The ovaries and the cement glands open by small apertures into a 

 large space, the brood cavity, occupying the space between the 

 outer and the inner sacs. Here the ova undergo their early develop- 

 ment, and as Nauplii pass forth through a well-marked opening, the 

 cloaca (d.y Figs. 1 and 2, PL 5) possessed of a strong closing or 

 sphincter muscle. Externally the cloacal aperture is obvious as a 

 prominent papilla. 



The young issue forth as fairly typical Nauplii, but differ from 

 those of Lepas and Balanus in being destitute of paired eyes, mouth, 

 and alimentary canal ; a central cellular mass, the rudiment of the 

 ovaries, is conspicuous. The Cypris-stage, into which the larva 

 enters after its fourth moult, also resembles a normal Cirripede 

 Cypris-larva, but deviates also in the absence of alimentary canal and 

 paired eyes. To this point the larval history is that of an ordinary 

 Cirripede, and by this fact alone are we enabled to class Sacculina 

 definitely as a Cirripede Crustacean. Without such knowledge it 

 would be practically impossible to properly access its position in 

 nature's scale. 



After a short free life, the Cypris-larva attaches itself by the 

 anterior antennae to the base of a seta or bristle upon the abdomen of a 

 young crab. In Jersey, I find Cancer pagurus (the edible-crab) to 

 be the most frequently attacked ; Pilumnus hirteUus is also com- 

 monly infested. On the other hand, I scarcely ever see Carcinus 

 mcenas attacked, and this is strange, as elsewhere this species is 

 credited with being the favourite haunt of the parasite. 



Following upon attachment, the thoracic region and its limbs, 

 together with the abdomen, are severed and thrown away ; the head 

 appendages wither arid the cellular mass which alone remains of the 

 contents of the Cypris-valves, secretes a containing bag-shaped cuticle, 

 marking the formation of the Kentrogon larval stage ; the Cypris- 

 valves fall away ; a second cuticle forms within the first cuticle of the 

 kentrogon sac ; the anterior end is produced into a hollow arrow-like 

 .process, which, passing forwards through the cavity of the anchoring 

 antenna, forces its way into the body of the crab-host. Through this 

 channel the contents of the sac pass, and then become surrounded by 

 a fresh cuticle. From this sac are thrown out branched roots rami- 

 fying in the course of time among the whole of the organs of the 

 crab. . 



