398 



EMBRYOLOGY OF INSECTS AND MYRIAFODS 



muscles, and a dorsal and ventral trachea pass. The recurrent nerve 

 arising from the posterior end of the bridge owes its origin to ganglion 

 cells which developed from the median dorsal wall of the stomodaeum 

 where it remains under the muscle layer. At the time the cardioblasts 

 meet on the middorsal line, small cells are liberated from the ectoderm 

 immediately above the heart to form a nerve that later attaches itself to 

 the heart (Fig. 349, dr). This nerve is formed independent of either 

 the central nervous or the visceral systems. 



The Tomosvary sense organs connected with the brain and located in 

 the head have been described for Scolopendra, Glomeris, Lithohius, and 



op.n 



neur.pl fg 



Fig. 354.- — Scolopendra cingulata. Cross section of foetal head, {ao) Aorta. (Jg) 

 Neuropile of frontal ganglion, {ggl) Ganglion cells, {md) Mandible, {mus) Muscle. 

 {neur. pi) Neuropile of deutocerebrum. {neur. p2) Neuropile of frontal lobe. {op. n) Optic 

 nerve, (tdm) Tomosvary organ, {torn, n) Tomosvary nerve. {Adapted from Heymons.) 



other myriapod genera. In Scolojpendra the organ is closely associated 

 with the development of the frontal lobes of the forebrain. Near the 

 frontal lobes, which owe their origin to the lateral brain pits, there is an 

 inward migration of some cells that closely resemble those of the frontal 

 lobes and that remain attached to the epidermis for a time. These 

 cells represent the anlage of the Tomosvary organ. As development 

 proceeds, the organ loses its connection with the surface but retains its 

 connection with the frontal lobe by means of a string of cells. This 

 string becomes the Tomosvary nerve which joins the brain at the junc- 

 tion of the optic and frontal lobes (Fig. 354, torn. n). The function of 

 these organs is unknown. 



The anlagen of the four pairs of eyes (stemmata) appear dorsad and 

 somewhat behind the insertion of the antennae. At the place where 

 they are to be formed the nuclei of the epidermal cells assume a basal 

 position and lie in a single plane. The cells around the margin of each 

 eye merge gradually into the adjacent epidermal cells. 



