158 THE CRUSTACEA 



nected by a median tendinous part which passes under the stomach 

 in the region of the maxillae. The muscle is innervated from the 

 maxillary ganglion. 



Nervous System. The brain is complex, admitting of close 

 comparison with that of other Malacostraca. The oesophageal 

 connectives are short and are united by the commissure of the 

 antennal ganglia behind the oesophagus. In the ventral chain the 

 ganglia of the mandibular, maxillular, and maxillary somites are 

 distinct, though, like the eight thoracic ganglia, they are closely 

 crowded together. Six abdominal ganglia are present, the seventh 

 somite, like the telson, having no ganglion in the adult. In the 

 embryo, however, a transitory seventh abdominal ganglion has been 

 found. 



Sense-Organs. The eyes are stated to resemble, in their intimate 

 structure, those of the Mysidacea. In Nebaliella and Nebaliopsis 

 and in one species of Nebalia (N. typlilops) the eyes are vestigial, 

 though the peduncles persist. On the upper and inner surfaces of 

 the ocular peduncle, in Nebalia, there are two small tubercles, 

 supposed to be sensory organs. Olfactory filaments of the usual 

 type are present on the antennules and, in the male, also on the 

 antennae. 



Reproductive System. The most conspicuous external difference 

 between the sexes consists in the much greater length of the 

 antennal flagellum in the male. The gonads have the form of 

 paired tubes extending, when mature, through nearly the whole 

 length of the body. The short vasa deferentia open on papillae on 

 the coxopodites of the last thoracic limbs. The oviducts are hard 

 to detect, but they appear to open on the sixth thoracic somite. 

 The spermatozoa are spherical and are aggregated into globular 

 spermatophores. The eggs are carried, as already stated, between 

 the thoracic feet of the female. 



Development. The development of Nebalia takes place within 

 the brood-chamber of the parent without any free-swimming larval 

 stages, and presents many points of resemblance to that of the 

 Mysidacea. The first three pairs of appendages appear simul- 

 taneously, giving a well-marked nauplius stage. The remaining 

 appendages develop in order from before backwards. The embryo 

 becomes free from the egg-membrane at a stage when all the 

 thoracic appendages, and sometimes also those of the abdomen, are 

 marked off (Fig. 92). The carapace at this stage does not extend 

 beyond the second thoracic somite. When the young leave the 

 maternal brood-chamber they have attained, in all essential respects, 

 the structure of the adult. 



