OF THE EOTATOEIA. 471 



is also seen in Vermes ; and in general the organization of the nervous sy- 

 stem is much more in accordance with that of Cestoidea than mth that of 

 the lowest Crustacea. Leydig remarks the great similarity of the maxillary 

 apparatus of young DapJinice Tvdth that of some Eotatoria, but forgets that a 

 similar structui'e occm^s in many Vermes. On the other hand, there are no 

 Crustacea which can, like several Notonimatce, protrude the maxillary organs 

 as prehensile instruments ; yet it is a common phenomenon with many Vermes. 

 Further, in no Articulata are the anus and rectum wanting, as happens ^^dtli 

 some Rotatoria ; for although in the larva of Myrmeleo, as Leydig states, the 

 rectimi is transformed into a spinning organ, still the viscus is present, though 

 modified for a different functional pui-pose : however, among Vermes such 

 an imperfect intestinal canal is common enough. From the preceding con- 

 siderations, the structui^e of the alimentary tube must be admitted to accord 

 rather with that of Vermes than with that of Crustacea. 



The secreted solid matter in the cloaca of embryo Cyclops, compared by 

 Leydig to the ^' uiinary concretions " of Rotifera, is, however (unlike them), 

 produced originally of a green coloui', within a sac on each side of the intestine, 

 but subsequently becomes yellow, and is discharged through the cloaca. Such 

 sacs or cells have rather the signification of a liver, and are common among 

 Vermes. 



Leydig relies most on the phenomena of the sexual system and the occiu'- 

 rence of distinct male animals. But PoJynoe, Exogone, and the Cystoneidce 

 produce both summer and winter ova, and carry them about. And with re- 

 ference to the existence of small distinct males, Krohn has proved it in Au- 

 tolytus prolifer, whilst among Xematoid worms generally a marked difference 

 obtains between the males and females ; and what, indeed, can be more 

 striking than the difference between Distoma Okenii and D. hcBmatohium ? 

 The variation in form and structure between the two sexes can therefore 

 furnish no differential character, seeing that it occurs ahke in some Crustacea 

 and in most bisexual Vermes. 



The occurrence of a metamorphosis, and the shrivelling or obliteration of 

 the eyes, are phenomena common to Vermes and Cnistacea. The lai-val Ste- 

 phanoceros is equally comparable and similar to the occasional type of Annelid 

 larva, having a frontal cUiaiy wreath in advance of the eyes, or otherwise to 

 the larvae of Nemertidix, such as Alardus caudatus, as to the embryos of any 

 Crustacea. Wherefore all Leydig's characters, even where they indicate 

 some afiinity with the Crustacea, exhibit, at least, an equally close one with 

 Vermes. 



The presence of vibratHe cilia and the peculiar respiratory organs are, as 

 Leydig admits, circumstances approximating Rotifera to Annehda. A tor- 

 tuous canal mth cihated tags occurs in none of the Ai^ticulata, and is incon- 

 sistent with the type of their water-breathing apparatus. At best there is 

 only a remote analogy, whilst a close similarity, and even an identity, is seen 

 between such stmctures and those of most Cestoidea. 



The history of development is in favour of the Annelid alliance, and op- 

 posed to Leydig's hypothesis ; for in all Crustacea the embryo originates 

 from a primitive part superposed upon the yelk, whilst in Rotifera, in com- 

 mon with all Vermes, such a supplementary part is wanting, and the embryo 

 is generated from the entire yelk. 



The appeal to metamorphosis lends its support to the present argument : 

 for no trace of resemblance is perceptible between the larvae of such Crusta- 

 ceans as undergo transfonnation, having three pairs of jointed legs or feet, and 

 the embryo stages of Rotatoria — for instance, of Stephcmoceros, with ciliaiy 

 wreath, posterior bimch of cilia, lateral eyes, and vermifomi trunk ; yet in 



