ECTODERMAL DERIVATIVES 103 



(Striridberg, 1913) it is unpaired, but just before hatching it assumes a 

 lateral position. 



The stomatogastric system in Pieris, according to Eastham (1930a), 

 arises at two points in the dorsal wall of the stomodaeum in a median 

 line. The stomatogastric (stomogastric) nerve is produced by extension 

 of nerve cells from the two ganglia along the roof of the stomodaeum. 



Among the Hymenoptera we have brief accounts of the development 

 of the system in Chalicodoma (Carriere and Biirger), in Formica (Strind- 

 berg), and in A'pis (Nelson). In the first both the unpaired occipital 

 ganglion and the paired pharyngeal ganglia are feebly developed; in the 

 second Strindberg failed to find either of these; in Ayis the second stomo- 

 daeal invagination gives rise to the frontal ganglion, whereas from the 

 third the pharyngeal ganglia originate. 



Relatively few references to the development of the stomatogastric 

 system in the Coleoptera are to be found. The frontal ganglion with its 

 recurrent nerve, according to Heider (1889), originates from a furrow- 

 like invagination of the stomodaeum, but Wheeler (1893) refers only to 

 the frontal ganglion. Strindberg states that the frontal ganglion as 

 well as the pharyngeal ganglia in Chrysomela arises in the usual manner. 

 The occipital ganglia in this insect seem to be represented by two small 

 cell masses located at the morphological anterior margin of the syncere- 

 brum. In Calandra oryzae the stomatogastric system arises as three 

 invaginations, according to Tiegs and Murray; Wray notes but one in 

 C. callosa. 



The Brain. — The composite suprastomodaeal nerve mass constitutes 

 what is generally known as the "brain," or "archicerebrum." At the 

 anterior end of the young arthropod embryo is a large cephalic lobe the 

 neural elements of which may include an anterior median ganglionic 

 rudiment and several pairs of lateral rudiments which soon unite to form 

 the brain. In the cephalic lobe there is no external mark of segmentation . 

 The definitive brain of the mandibulate arthropods consists of an anterior 

 bilobed part, including the protocerebrum, the deutocerebrum, and the 

 tritocerebrum. The first innervates the eyes; the second, the antennae; 

 and the third, the second antennae when these are present. The proto- 

 cerebrum and the deutocerebrum are always united above the stomo- 

 daeum, but the tritocerebral lobes, being derived from the postoral 

 somites of the second antennae, are connected by a postoral commissure. 

 In many cases the dorsal lobes are developed in the embryo from a single 

 pair of generative centers in the ectoderm just as are the corresponding 

 lobes of the brain in the Onychophora and in some of the Annelida; but 

 since the annelid brain probably originated from a number of prostomial 

 ganglionic centers corresponding to the sensory organs of the prostomium, 

 one may reasonably expect the primitive arthropod brain to show a 



