240 BUMPUS. [Vol. V. 



tion (Scg 2 ), which, it seems to me, may have considerable 

 morphological importance. The ganglionic mass at the base of 

 the primitive compound eye is divided into an anterior and a 

 posterior portion (G. 1 , G. 2 ). The anterior is more directly impli- 

 cated in the optic tract, while the posterior, which probably 

 answers to the cerebrum of the adult, is possibly primarily asso- 

 ciated with the crescentic elevations already noted. Though 

 these lateral elevations soon disappear, the cerebral lobes in- 

 crease in size with the developing embryo. 



If we allow the compound eyes to occupy the position of a 

 pair of pre-oral appendages (and their development, thus far, is 

 not different from that of the antennae, though I am well aware 

 of the position held by many morphologists upon this mooted 

 point), and if moreover the crescentic folds represent a second 

 pair of pre-oral appendages, no longer present in the adult, the 

 stage under consideration is most suggestive, since five pairs of 

 ganglionic swellings are then present, each presiding over a dis- 

 tinct segment, while the ganglia of either side are united as 

 shown in the figure by a longitudinal connective (Nc). The 

 stage is strikingly annelidan and, when taken in connection 

 with the approach of the two divergent halves towards the 

 median line, it would seem that we have a case of concres- 

 cence comparable with that presented by Lumbricus (Wilson, 

 '89), and by Clepsine as described by Whitman ('78). The part 

 played by the U-shaped mesoderm is further evidence of con- 

 crescence of Homarus. 



The second antennae are not as yet elevated to any consider- 

 able extent above the general surface of the egg, and their 

 slightly smaller ganglia would point to a somewhat tardy devel- 

 opment. Suggestions of the definitive joints are present. 



The jaws, or mandibles, are somewhat smaller than the "sec- 

 ond " pair of appendages. A longitudinal elevation or ridge 

 (.Nc.) marks the connective joining the mandibular ganglion 

 with the ganglion of the appendage just described, while at the 

 posterior edge occurs an abrupt concavity which surrounds the 

 elevated thoracico-abdominal fold. The formation of this fold 

 from the immediately preceding stage is as follows : The pinching 

 together of the lateral lips of the blastopore results in the forma- 

 tion of two parallel nucleated masses (PI. XVI, Fig. 3) which 

 finally meet in the middle line over the still slightly open blasto- 



