NEUROSECRETION 



1059 



influences and regulates the secretory activity of 

 tiiese organs. 



Neurosecretory Activity in Various Classes of Invertebrates 



VERMES. The annelids represent the first class of 

 invertebrates to exhibit significant patterns of neuro- 

 secretory acti\ity. Neurosecretory activity has not 

 been observed in the coelenterates and has not been 

 established with certainty in the flatworms. In the 

 free and sessile polychaete annelids, neurosecretory 

 elements exhibiting pcssible cyclic secretory activity 

 have been found in the cerebral ganglion and in the 

 ventral nerve cord (13, 274). Although there are no 

 notable sex differences, the neurosecretory phenome- 

 non in nereids does undergo changes correlated with 

 reproductive activity (93, 276). In Lumbricus, neuro- 

 secretory cells have been observed in the cerebral 

 and esophageal as well as in both anterior gastric 

 ganglia, with neurosecretory material being trans- 

 ported as far as the fourth gastric ganglion (60, 154, 

 158, 277). In Lumbricus also there appear to be func- 

 tional relationships between the neurosecretory ele- 

 ments and the reproductive apparatus (alpha cells) 

 as well as to regenerative phenomena (beta cells) 

 (175, 176). In the group of sipunculids, neurosecre- 

 tory elements are found in the brain of Fasculosoma 

 vulgare, extracts of which act to slow down the con- 

 tractions of the nephridia (185, 313). In five species 

 of Onychophora, neurosecretory activity has been 

 observed in the cerebral ganglion as well as in the 

 ventral nerve cord. In these forms, the secretory 

 activity may be cyclic, but there is no notable evidence 

 of transport of secretory material or participation of 

 the nucleus in the secretory activits' of the cell (113). 



ECHiNODERM.M A. Neurosecretory acti\ity has not been 

 oijserved in this phylum of invertebrates. 



MOLLUSCA. In 25 species of prosobranchs which have 

 been investigated, neurosecretory elements are ex- 

 ceedingly variable with the supraintestinal and pleural 

 ganglia exhibiting evidence of secretory activity most 

 frequently. In 35 species of opisthobranchs, evidence 

 of neurosecretory activity has been observed most 

 consistently in the cerebral ganglion. In both classes 

 of animals, the seasonal variation in neurosecretory 

 activity appears to be related to the maturation of 

 gonadocytes (107, iio, iii, 275, 277). A uniformity 

 has been found in the lamellibranchs where the 

 cerebral and \isceral ganglia have consistently ex- 

 hibited neurosecretory activity and the pedal ganglia 



none (119). The secretory phenomena of the peduncu- 

 lar and epistellar glands of the cephalopods is not 

 considered authentic neurosecretion (i 19J. 



.ARTHROPODS. The morphological aspects of neuro- 

 secretion have been most extensively investigated in 

 this phylum of invertebrates, and accordingly the 

 greatest insight into its functional role has been gained 

 here. Studies on the decapod crabs have shown the 

 neurosecretory cells to be present in the brain and 

 especially in Hanstrom's organ of the eye stalk, the 

 axons of which join in a common path and end in 

 the sinus gland. Historically these cells were the first 

 neurosecretory elements described in invertebrates 

 (146). In the sinus gland, the enlarged terminations 

 of these nerve fibers assume a relationship to a central 

 blood cavity (50-52, 64, 65, 147, 248). These neurons 

 contain granular inclusions which may coalesce to 

 form larger complexes which are visible in unstained 

 preparations and which can be stained specifically 

 with chromhematoxylin. Numerous mitochondria are 

 present in these cells and are readily differentiated 

 from the neurosecretory material (249). A minimum 

 of three different types of secretory neurons have been 

 distinguished. The sinus gland is considered as a 

 reservoir for the several kinds of neurosecretory ma- 

 terial delivered to it from these cells. Removal of the 

 entire eye stalk leads to increased respiration, a fall 

 in respiratory quotient and water intake. These 

 changes do not occur when the sinus gland alone is 

 removed leaving intact and functional those neuro- 

 secretory cells in the brain producing the eflfective 

 hormones. After transection of the tract from the 

 x-organ to the sinus gland, there occurs initially a 

 depletion of the neurosecretory material at the site 

 of the cut, followed later by a complete regeneration 

 of the sinus gland (47, 48, 52, 99, 247). Along with the 

 regeneration of the sinus gland, there is said to be a 

 complete restitution of its functional activity (52). At 

 least three chromatophoric hormones and other 

 substances exerting an influence on the pigments of the 

 eye are .said to be formed in the ganglia optica in 

 addition to those substances which regulate molting, 

 and calcium and water metabolism. Bliss (49) has 

 investigated the role of this system in growth and 

 regeneration as well as the influence thereon of light, 

 temperature and other conditions. The tritocerebral 

 commissure constitutes a second center containing 

 neurosecretory elements extracts of which influence 

 the chromatophoric hormones (182, 185). In certain 

 diplopods, members of the class Mvriapoda, specific 

 axons demonstrable with chromhematoxylin are pres- 



