PALINURUS OR THE SPINY LOBSTER OF BOMBAY. 387 



This pouch, the primitive gut or archenteron (Gr. arche, origin, 

 primitive state, enteron, gut) continues to deepen and its mouth to 

 contract till we get a completely closed sac. 



The cells lining the primitive gut are known as the hypoblast or 

 endoderm (Gr. hypo, under, endo, inner). The remaining cells of the 

 blastoderm are the epiblast or epiderm (Gr. epi, above) from which is 

 eventually developed the epidermis of the integument, of the fore-gut, 

 of the hind -gut and the nerve system. A mass of cells appears between 

 the hypoblast and epiblast near the blastopore, probably derived from 

 the former ; from it the muscles, connective tissues, heart, vessels and 

 reproductive organs are developed. It is called the mesoblast (Gr. 

 mesos, middle). 



In front of the blastopore, before it closes an elevation appears 

 which lengthens in a forward direction. This is the rudimentary 

 abdomen. In front of this again a pair of flatter elevations appear 

 one on each side of the middle line called the head lobes. A median 

 linear depression appears on the surface of the epiblast between 

 these three elevations. Near its centre the groove deepens into a 

 tubular ingrowth, the stomodamm, as already described. The 

 primitive hind-gut arises in a similar manner on the abdominal 

 papilla. A considerable time elapses before the partitions between 

 the three portions of the gut disappear. The appendages appear as 

 symmetrical pairs of buds of the epiblast and mesoblast. Those of the 

 antennules, antennae and mandibles appear early. The eyestalks 

 appear later as outgrowths of the head lobes. 



The epiblast on each side of the median ventral groove thickens 

 in two longitudinal strands to form the double nerve chain, which 

 later severs its connection with the tegumentary epiderm. 



The eggs of many Crustacete, for instance Penaeus, one of the 

 Prawns, are hatched in an elementary stage with only the three 

 anterior pair of appendages, which become very large and are 

 used in swimming. This is known as the Nauplius stage. In 

 Palinurus as in Lobsters, Crayfish, the Prawn, Palannon and most of 

 the other Macrura (Gr. longtails) this stage is passed inside the 



egg- 



Owing to the fact that the larvae of Palinurus are inhabitants of 

 the open sea, the full course of their development has not been 

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