MOKPHOLOGV or THE C'OPEPODA. .'39S} 



ceutuiy^ together Avitli the investigation of its organization 

 {vide particularly R. Leuchr.rt, "Einige Beraerkungen iiber 

 Sacculina, Thomps/' TroscheFs ' Arehiv/ 1859)^ wliicli first 

 aftbrded the proof of the Lernpean nature of this remarkable 

 .Arthropod. 



Consequently^ in the multiple forms of parasitic Crustacea 

 we find an almost uninterrupted series of gradual transitions, 

 from the stage of organization presented in the free-swimming 

 Copepods down to the sacciform Sacc?dm(i, Avhich exhibits no 

 trace of segmentation nor of segmental appendages. The 

 segmentation of the Cyclopidpe is most completely represented 

 in the family of the Ergasilina, in Nicothoe, Bomohchus, Er- 

 i/asUus, &c. BomolocJms, Doi'idicola, and Chalimus, in the sen- 

 tiform development of the thorax, point to the families of the 

 Caliginfe and Pandarinse ; whilst Ercjasilus, Fagodina, Eudac- 

 tyUna, Nofopterophoi'us, and Notodelplds, from the more 

 delicate structure of the carapace and more extended form of 

 the body, approach the Dichelestiniin?e. At a lower stage we 

 find a fusion of the abdominal rings and abortion of the abdo- 

 men, as in Kroyeria, Ccdigus, ScicenopMIus; Nogagus, Dine- 

 mura, Pandarus, Cecrops, Lmmargus, Lamproglene. A further 

 retrogression is manifested in — 1, the absence of thoracic feet, 

 with a complete segmentation of the thorax itself — DicJielesthim, 

 Anthosonia ; 2, in an imperfect division into somites of the 

 thorax, a, accompanied Avith transformation of the last pair 

 of limbs into saccular processes — Clavella ; c, with a simulta- 

 neous transformation of tlie anterior thoracic members into 

 imjointed sacculi — Choiidracantlius. In a still furtlicr stage of 

 degradation, together with the complete absence of an abdo- 

 men, the thoracic members are entirely wanting — Leniaopoda, 

 — whilst the last cephalic mem])ers, the second jaw-feet, arc 

 degraded into an unjointed appendage, and fused into tht^ 

 well-known adhesion-organ. At first the two anterior thoracic 

 somites are still apparent as distinct rings — Lernceopoda GalVi ; 

 but all appearance of division in the thorax disappears, which is 

 distinguishable from the head only by a sharpish border, as in 

 the Chondracanthce, TracheUastres, Brachiella, Anchor eUu,S<,c. 

 In the Lerneeocerfe and Lernseee, the anterior jaw-feet are 

 also reduced to hook-like prominences, whilst the fusion and 

 transformation of the posterior pair into an organ of adhesion 

 no longer exist. But, beyond this, the complete dis- 

 appearance of both these members, together with that of the 

 mcuvilke and puljn, marks the transition to the last and lowest 

 stage, which among the parasitic Crustacea is represented by 

 the Trematode-like Sacculina, Thomps. 



If we throw the results of our considerations into a general 



