CRANGON VULGARIS. 23 



In flg. 42 the ganglia of the ventral thoracic chain are al- 

 reacly seen to be differentiated by the appearance of fibrous 

 portions (dotted in the figure), while no such structure is 

 visible in the abdomen. Here, however, the ganglia are 

 separated by the rudimentary flexormuscles (mw) extend- 

 inof downward to the ventral snrface. From sections 46 

 to 49, we See that in stage G there are a cerebral ganglion 

 proper and two antennal ganglia in front of the mouth ; a 

 count of those shown in fig. 42 shows sixteen in the ven- 

 tral chain, of which seven are abdominal, a total of nine- 

 teen, leaving two to be added to the thoracic region. 



In stage H (hgs. 54-71) tliere is a considerable advance, 

 represented diagrammatically in the last figure (71). In 

 54 we see that the brain is of considerable size, and that 

 two of its masses of transverse commissural fibres are 

 large. Behind the mouth and Oesophagus the ventral chain 

 is well shown nearly to the anal opening. Itis, however, 

 noticeable that nowhere has it yet separated from the par- 

 ent ectoderm. 



In the cerebral region several featuresmaybementioned. 

 In fi«:. 55 transverse commissures are seen connectin«: to- 

 gether the two members of the first pair of ganglia. Three 

 sections back (fig. 56) we see two bands of fibres the 

 outer of which (/b), as the next figure shows, is connected 

 with the eye, while the other {fc) can be traced in the sec- 

 tions not figured, to the cm' of fig. 55. In figs. 57 and 

 58, the latter a more magnified representation of the for- 

 mer, a process is clearly seen which I interpret as a break- 

 m^ down of certain of the sranHion cells and their nuclei 

 and a modification of the protoplasm into nerve fibres. In 

 the centre of fig. 57 (cm^) is seen the section of a second 

 commissure uniting the two halves of the "brain," while 

 in fig. 59 (two sections farther back) , these are again sep- 

 arated (cv) and serve to connect the two ganglia of the 

 same side and the anterior bend of the Oesophagus and its 



