CHOXDRACAXTHUS GIBBOSUS. 24:1 



seems to be connected with a subjacent ganglionic mass. 

 The body is sufficiently transparent to allow the pulsations 

 of a heart to be seen, but none can be discovered. The testis 

 is a large oval bilobed mass (^), lying like a saddle upon the 

 anterior part of the intestine. From this body a thick vas 

 deferens runs back upon each side of the intestine, and di- 

 lates in the penultimate and antepenultimate somites into a 

 thick walled pyriform sac — a sort of vesicula seminalis. The 

 embryo leaves the egg as a Kauplius^ like that of Cyclops. 



There are many genera of these parasites, some of which, 

 such as the almost completely vermiform LerncBC^^ deviate 

 even more widely than Chondracanthus from the ordinary 

 form of Ci'ustacea^ while others, such as Ergasilus and Noto- 

 delphys^ differ but little from the free Copepoda. 



In Caligus, the labium and metastoma are elongated and 

 united into a tube in which the sharp styliform mandibles are 

 inclosed ; and from the prevalence of this suctorian form of 

 mouth in some of the best known species of parasitic Cope- 

 poda,, they are frequently termed "suctorial" crustaceans. 

 Suctorial disks for attachment are developed from the coa- 

 lesced posterior pair of thoracic members in Achtheres ; and, 

 in this genus, the head, as a distinct part, becomes almost 

 entirely obsolete. 



Argulus, the parasite so common on the Stickleback, is 

 worthy of notice as one of the most curious modifications of 

 the epizoic t^^pe.^ It is extremely flattened, and is composed 

 of an anterior cephalo-thoracic disk, behind which lies a very 

 short and broad, notched abdomen. A median styliform 

 weapon lies in a sheath in front of the mouth, and the small 

 mandibles and maxillae are inclosed in a short tube formed 

 by the labrum and the metastoma. Six pairs of appendages 

 lie behind the mouth, the anterior being metamorphosed into 

 suckers, the next pair into strong limbs with a toothed sec- 

 ond joint, and the four others constituting biramous swim- 

 ming-feet. There are two pairs of antennary organs, and two 

 compound eyes. According to Leydig, the males are pro- 

 vided with cups on their penultimate sw^imming-feet ; and, 

 during copulation, these are filled w^ith the seminal fluid, 

 which is thus transferred to the vulva of the female, and 

 thence to the spermatheca. The eggs are laid, and not car- 

 ried about in ovisacs. The larva is provided with two pairs 



1 Claus (" Ueber die Entwickelansr, Orsfanization und systemati^^ehe Stelkmg 

 der Arsruliden," 1875) has proved the close affinity of Argulus with the Cope- 

 poda,, but proposes to regard it as the type of a special group, the Branchiura. 



