MUSEUM OF COMPARATIVE ZOOLOGY. 



327 



EXPLANATION OF THE PLATES. 



The appendages, from the first to the last pair, are indicated throughout by 

 consecutive Roman numerals. They correspond with the appendages of the 

 adult as follows : — 



J, first antenna. 

 II, second antenna. 



III, mandible. 



IV, first maxilla. 

 V, second maxilla. 



VI, first maxilliped. 

 VII, second maxilliped. 

 VIII, third maxilliped. 

 IX, first pair of legs (cheliferous). 

 X, second " " 



The Arabic numerals denote the somites of the abdomen. 



XI, third pair of legs. 

 XII, fourth " 



XIII, fifth - " 



XIV, first pair of abdominal appen- 

 [dages. 



XV, second 

 XVI, third 

 XVII, fourth 

 XVIII, fifth 

 XIX, sixth 



a b, abdomen. 

 a r, artery. 

 c d, cephalic disk. 

 cp, carapace. 

 h t, heart. 

 i n, intestine. 

 I b, labrum. 

 m, mouth. 



ng, nerve-ganglion. 

 o c, compound eye. 

 ocl, ocellus. 



r e, external branch of appendages. 



r i, internal " " 



rs, rostrum. 



t, telson. 

 v t, yelk. 



Plate I. 



Fig. 1. Egg with four segments produced by an equatorial and a meridional 

 cleavage. Each segment contains a nucleolated nucleus (n), around 

 which delicate lines of protoplasm are disposed like rays. 



Fig. 2. Egg with sixteen cleavage spheres. 



Eig. 3. The surface of the yelk is now divided into small polygonal blasto- 

 meres. g, orifice of gastrula-cavity. 



Fig. 4. Profile view oi the embryo, four days after the gastrula-stage. The 

 appendages have appeared from the first to the sixth pair. Except- 

 ing the first pair, they are bilobed or double. 



