36 MICROSCOPICAL STUDIES. 



these limbless thoracic somites, and as time goes on, the true 

 abdominal somites appear at this point of junction and simul- 

 taneously tiny limbs sprout out from these newly formed parts. In 

 Fig. 3 two pairs are shown in an early sprouting stage. This, the 

 Erichthus or Glass Shrimp stage, was long mistaken as representing 

 a separate animal, and before going further, let me point out why it 

 does not receive the name of Zoea, as the young larvae of the 

 Decapods are so well known by. 



If the newly hatched young of the Common Shore Crab 

 (Garcinus) be examined they will be seen to possess apparently 

 the same body parts as the Squilla Erichthus. A large carapace 

 covers the fore part of the body, and a tail unprovided with limbs 

 follows, ending too in a broad telson. Yes, but here most curiously, 

 the hinder part of the thorax is not yet in any way recognizable, and 

 the tail portion is true abdomen and not thorax as in Squilla ; seven 

 pairs of appendages are present ; the two pairs of antennae, the 

 mandibles, two pairs maxillae and two pairs of maxillipeds. The 

 third pair of the last named organs and the whole of the am- 

 bulatory limbs are absent and when they do appear, they sprout 

 out from the point ^-r~2^ J us ^ an t er i r to the 



junction of thorax ^^^^^/'''/^ with abdomen. The 



swimmerets appear ^5^3*^ \ about the same time 



as paired buds from ">^$?|8. ) the segments of the 



tail-like abdomen. ^fl/^^^h^M Thus there is a wide 



divergence between p$J^ ^O? the Zoea and the 



Erichthus. In the TS> \*S one, the abdomen is 



present from the ^\Str-~^ s= nrs t,while the hinder 



part of the thorax '^SL_ is absent in the 



other, the cepalo- ADVANCED ZOEA OF A CBAB. thorax is present in 

 full segmental number from the beginning, but the abdomen is 

 wanting, saving for the telson. 



After several moults the Erichthus loses entirely the three 

 hinder maxillipeds, while synchronously the tiny abdominal somites 

 that have just appeared, develop their bud-like limbs into large 

 biramous swimmerets or pleopods, while each of the second maxil- 

 lipeds increases in size quite disproportionately to its neighbours 

 and becomes a huge somewhat chela-like limb differing however 

 from the true chela or pincer form (seen so well in the Lobster) 

 in that the terminal joint is not opposable to an outgrown, huge 

 finger-like spine of the second, but instead folds down upon the 

 second, fitting when at rest, into a deep groove running along the 

 inner margin of this penultimate joint. In the adult the edges of 

 this groove are beautifully sculptured with most delicate serrations, 

 and in the larvae show also, but in a coarser form (PI. vi, Fig. 4). 



