JOURNAL OF MICROSCOPICAL SCIENCE. 



EXPLANATION OF PLATE VI, 



Illustratiog the Abstract of Reichenbacb's Paper on the 

 Development of the Crayfish. 



References. 



A. Thoracico-abdominal process. 

 At. I. Antennules. 



At. II. Antennae. 

 an. Anus. 



B. Rudiment of carapace. 

 G, Blastopore. 



H. Endodermal plug which partly 

 fills up the blastopore in stages 

 II and III. 



N. Position of heart. 



K. Proceplialic lobes. 



KS. Head-discs. 



Ml. Mandible. 



Oe. Mouth. 



R. Medullary groove. 



V. Optic fossae or depressions in the 



head-discs which form the optic 



ganglia. 



Fig. 1. — Embryo in the first stage, with horse-shoe shaped blastopore. 



Tig. 2. — Embryo in the second stage, with annular blastopore. 



Fig. 3. — Embryo in the third stage, with procephalic lobe, optic fossae, 

 medullary groove, and deccussing blastopore. 



Fig. 4. —Embryo in the fourth stage, with increased thoracico-abdominal 

 process and greatly reduced blastopore. 



Fig. 5. — Embryo in the fifth stage, with commencement of fore and hind- 

 gut, rudiments of mandibles and of carapace, and closed blastopore. 



Fig. G. — Embryo in the sixth or Nauplius stage, with antennules, an, 

 tennse, and mandibles, well-formed mouth and anus, and no trace of 

 blastopore. 



