292 



GLOSSAET. 



Repetition. When there occurs a succession of similar pr.rts in 

 the same animal, as in the centipede. 



Retina. The third tunic of the eye, formed by an expansion of 

 the optic nerve. 



Retinaculum. A minute scale or plate which checks the too great 

 protrusion of the sting of certain insects. 



Reversion or Atavism. When a character reappears in an indi- 

 vidual animal which had disappeared for some preceding gene- 

 rations. 



Rhachis. The axis of a feather. 



Rudimentary organs. Parts which have been gradually atrophied 

 owing to disuse. A rudimentary part is larger comparatively 

 in the embryo than in the adult. 



Sacrum. Anchylosed vertebras, to which, on each side, the pelvic 

 bones are attached. 



Sarcoblasts. The " yellow cells " of the Eadiolaria. 



Barcode. See Protoplasm. The term is most frequently applied 

 to the protoplasm of the Protozoa. 



Sarcolemma. " The elastic tunic of the striped muscular fibre." 



Scape. (1) The basal joint of the antennas of insects when un- 

 usually developed, (2) The axis or rhachis of a feather. 



Schizocale. The perivisceral cavity that results from the split- 

 ting of the mesoblast. 



Sclerenchyma. Coral tissue. 



Sclerobase. A form of skeleton in the Alcyonaria " formed by 

 the cornification or calcification of the axial connective tissue 

 of the zoanthodeme " (Huxley). 



Sclerotic. With the cornea the exterior tunic of the eye; in 

 many of the Vertebrata it is ossified. 



Scolex. The second larval stage of a Cestode worm when it has 

 encysted itself. 



Scrobe. A groove in the rostrum of certain Coleoptera for tl 

 reception of the scape. 



Scutellum. The posterior part of the mesothorax of insects 

 from above. It is variously modified, but in Coleoptera it 

 triangular. 



Scutes. The bony scales of the Crocodilia. 



Scyphistoma. A form developed from the hydra-tuba of certaii 

 Hydrozoa ; it afterwards passes into the strobila stage. 



