52 



ON CLASSIFICATION. 



thought it probable that these " pseudo-haemal " vessels are ex- 

 treme modifications of organs homologous with the water-vessels 

 of the Scolecida. As M. de Quatrefages has clearly shown, it is 

 the perivisceral cavity with its contents that, in these animals, 

 answers to the true blood-svstem of the Crustacea and Insects. 



The embryos of Annelids are very generally ciliated, and 

 vibratile cilia are commonly, if not universally, developed in 

 some part or other of their organization. In both these 

 respects they present a most marked contrast to the succeeding 

 classes. 



Fig. 25. 



1v- 



Fig. 25. — Amphithoe, an amphipodous Crustacean. — Lateral view (A), longitudinal and ver- 

 tical section, detached appendages and stomach (C, D). The numbers I' to XX' indicate 

 the appendages of the corresponding somites, r. Lostrum. t. Telson. lb. Labium. 

 st. Roof of the head, or cephalostegite. os. Oostegite. Br. Branchiae. Stomach 

 opened from above (D), and viewed laterally (C). a, b, c. Different parts of the armature. 



