

Fl(i. OS. 



Di'velopiiiont of Clnthrina hlanca as seen in sections. 1, larva; 1"-1'', four stap's in tho 

 nioilitiuitioii and inmii^tration of a riliatoil cell into the inner mass ; 2, section of pnjMi after 

 completion of meUtniorpliosis (llrst day) ; 3, section of pujia on tlie second day. Tlio iminl^ra- 

 tion of cells from the dermal epithelium, to form the skoletogenous stratum, is goinn on actively, 

 tho porocytes are agnregated in the centre, and the gelatinous ground substance is making its 

 appearance. 4, section of pupa early on the third day. The gastral cavity, lined by imrocytes, 

 and the spicules have ai)peared. 5, section of pupa towards the eu<l of the fourth day. The 

 gastral cavity is lined by gastral cells, whidi are commencing to develop collars and llagella, 

 while their nuclei are migrating towards the bases of the c«m1s. The spicides are largi' ; the 

 position of the future oscubim is indicated ; the porocytes are migrating outwards ; and the 

 amoebocytes have changed in appearance, avi.c, ainoebocytes ; cil.c, ciliated cells; (!.V, 

 gastral cavity ; 0!>i; osculum ; ;).<-, porocytes ; jt.g.c, posterior granular cells ; skel, skoleto- 

 genous stratum ; .s;iiV, spicules. 



