EPizoA. 273 



buted to the head, and along each side of the commeneement of the 

 alimentary canal to the under part of the body, where it passes back- 

 wards in the vessel which accompanies the intestine. 



The ovaria at first appear in the form of a slightly flexuous, long, 

 blind tube, sacculated along one side {o,Jig. 116). As the ova are 

 developed, the ovarium takes on the form of a bunch of grapes, and 

 occupies the whole cavity of the abdomen external to the intes- 

 tine 6' : each ovarium terminates by a triangular, and somewhat pro- 

 minent orifice, to which the external ovisac (/) is appended. 



The Epizoa are remarkable for the disproportionate size of the 

 117 ^^ sexes. In the minute male {Jig- 117), the testes are 



indicated by four dark coloured and finely granulated 

 bodies {d d) situated in the posterior segment or 

 abdomen. He appears like a mere parasite of the 

 female to which he adheres, near the vulva, and 

 having usually one antenna inserted into that aper- 

 ture. 



The first remarkable circumstance in the natural 

 Achtheres, male. history of the aquatic Epizoa is the constancy with 

 Magnified. ^vhich particular species infest particular fishes or 



Crustacea. And how, it may be asked, can creatures so devoid of 

 means of transport, nay, in most instances, of the power of detaching 

 themselves from the animals whence, like foetuses, they derive their 

 means of growth, originally reach the precise species of animal and 

 organ to which they are habitually attached ? 



Are certain of the ova accidentally retained near the parent after 

 the rupture of the ovisac ; and do they there grow, like seeds of plants 

 fallen in a favourable soil ? Or, do some of the liberated ova, by a 

 happy fortuity, arrive at the appropriate organ of the appropriate 

 species ; and are they there accidentally retained until the prehensile 

 instruments are developed ? Such_hypotheses may be permitted in 

 reference to the ova of an Entozoon, which are developed by millions, 

 and need only gain an entry into the animal they may infest, or 

 which may be the common food of the species in whose intestine they 

 are adapted to exist ; but the ova are too few in the Epizoa, and the 

 parts to which they are attached are too exposed, to allow of the 

 supposition that their parasitic growth is dependent on such acci- 

 dental circumstances. 



MM. Audouin and Edwards appear to have been the first to 

 suggest that the sedentary Lern^an Epizoa might enjoy at a previous 

 period of existence locomotive powers, and the hypothesis was sup- 

 ported by the discovery, made by Dr. Surriray*, of the embryo of a 



* CCXL p. 401. 



T 



