214 



ONYCHOPHORA. 



the nephridia are left out of account. The muscles, with the 

 exception of those of the jaw, show no transverse striation. They 

 form a dermo-muscular tube composed of several layers of diagonal 

 and longitudinal fibres arranged in symmetrically distributed bands. 

 Here Ave have features which recall the Annelida far more than 

 the Arthropoda, in which the dermo-muscular tube breaks up into 

 separate groups of muscles distributed in a definite manner. The 

 body-cavity, on the contrary, in its origin (as a pseudocoele), as- 

 well as in its final development, is altogether Arthropodan in 

 character. This is also the case with the dorsal vessel, which is 

 connected by ostia with the pericardium, and thus with the pseudo- 

 coele, for the jjericardial space is, as in the Arthropoda, a part of 

 the pseudocoele, and is formed on the whole in the same manner 

 as that of the Arthropoda. The development of the body-cavity, 

 and its division into separate spaces in the embryo, may be 

 compared with what is found in the ontogeny of the Myriopoda 

 and the Insecta, and may thus be regarded as an important point 

 of agreement between Peripatus and these forms {i.e., the Arthropoda 

 generally). 



The nephridia seemed to be a specially strong bond of union 

 between Peripatus and the Annelida as long as we had to assume 

 that they opened, as in the latter, through a wide funnel into the 

 body-cavity (Balfour, Gaffron). But since it has become known 

 that they are closed by means of a vesicle towards the adult body- 

 cavity (Sedgwick), although their segmental repetition still offers an 

 important point of comparison with the Annelida, a still greater 

 inclination towards the Arthropoda is shown, the nephridia (antenna! 

 and shell-glands) in the Crustacea having the same form.* This 

 similarity of structure renders it probable that the nephridia of 

 Peripatus are no longer ciliated f; if, however, the statements that 

 have been made as to the presence of a ciliated epithelium in the 

 nephridia that are transformed in the efferent genital ducts J should 



11 [This vesicle or end-sac is a thin-walled remnant of the coeloni, homologous 

 with that of an Annelid, with which the nephridinm communicates by a thick- 

 walled funnel. The body-cavity of the adult Peripatus is a pseudocoele like 

 that of other Arthropoda, with which we should certainly not expect to find the 

 nephridia communicating. The nephridia of Peripatus are specially interesting 

 since they appear to combine certain Arthropodan features (the coelomic end-sac) 

 with others only met with in the Annelida (segmental repetition and marked 

 funnel). — El).] 



t We have not been able to find any definite statements as to the presence or 

 absence of cilia in the nephridia of Peripatus. 



J Gaffkon describes and figures a thickly ciliated epithelium lining the vasa 

 deferentia. 



