186 DREDGING REPORTS; 
The structure of the animal is of the most simple kind. An 
ovate, cylindrical, somewhat quadrate or subtriangular body is 
almost entirely filled with ova, which are contained either in a 
single sac, or in very numerous ramifying tubes. These with 
two elongate organs presumed to be testes, but which may 
possibly be cement glands, are almost the only organs which are 
recognizable either externally or internally. No trace of limbs, 
no vestige of manducatory, scarcely a sign of digestive, and none 
of respiratory organs, is observable. The young are excluded 
through a small orifice which is situated at some distance from 
the sucking disk; and through this orifice water is also admitted 
into the cavity of the body and among the eggs. The sucking 
disk varies considerably in size in the different species, and is 
either simple or margined with an extended border, or sometimes 
furnished with fine fibres, which, penetrating the tissues of the 
crab, imbibe nourishment from them by endosmose in a manner 
which reminds us not a little of the connection which exists 
between the misseltoe and the tree on which it grows, and from 
which it derives its support. It is not improbable that it may 
hereafter be proved that these penetrating tubular fibres are 
characteristic of all the species of this order. 
It would be impossible to assign to the Sacculinacea their 
right position in the animal kingdom from the mere examination 
of the mature form, and no animals have ever been more bandied 
about from one class to another than these parasites. The early 
stages and development of the young, however, clearly prove, as 
was first observed by Mr. William Thompson of Belfast, that 
the Sacculinacea are Crustacea; and if, in addition to the 
evidence afforded by the form of the first stage of the larva, 
which closely resembles that of the Cirripedia, the supposition 
of Lillejeborg be correct, that a cypris-formed case, which he 
observed attached to one extremity of a small Peltogaster, was 
the slough of the second stage of the larva still clinging to the 
animal which had been developed from it, there can be little 
doubt of the correctness of the theory which that eminent 
carcinologist has advanced, that these wonderful Trematoid 
parasites are an aberrant order of the sub-class Cirripedia. I 
