GLOSSARY 



493 



REGENERATION, RESTORATIVE - changes 



occurring in regular fashion after an acci- 

 dent, bringing about a replacement of lost 

 or damaged parts. 



REGENERATION, WOLFFIAN - appearance of 

 a new lens in the eye after removal of the 

 former lens, due to possible regeneration 

 from the upper margin of the iris. 



REGENERATIVE CAPACITY - the ability to re- 

 place lost parts, the ability which varies 

 (generally) inversely with the scale of de- 

 gree of development. 



REGION, PRESUMPTIVE - regions of the blas- 

 tula which, by previous experimentation, 

 have been demonstrated to develop in cer- 

 tain specific directions under normal onto- 

 genetic conditions (e. g. , presumptive noto- 

 chord or lens). Not as definite as anlage'. 



REGULATION - a reorganization toward the 

 whole; the power of pre-gastrula ennbryos 

 to utilize materials remaining, after partial 

 excision, to bring about normal conditions 

 in respect to the relation of parts; somewhat 

 comparable to regeneration of later stages, 

 but more flexible and more extensive in 

 early development. Ability to adjust to a 

 strange environment and yet to develop 

 along lines of normal development. 



REINTEGRATION - the restoration to the organ- 

 ism, after the period of self differentiation 

 and through the action of hormonal and 

 neural factors, of control by its individua- 

 tion field. 



RESONANCE THEORY OF REFLEX ACTIVITY - 

 the central nervous system can emit differ- 

 ent forms of excitation and a specific mus- 

 cle will respond only to the excitation ap- 

 propriate to it. Rather than different 

 conducting pathways for the central nervous 

 system and peripheral end organs (e. g. , 

 limbs), all components of an excitation are 

 transmitted to all muscles, but only that 

 muscle, for which a specific component is 

 contained, will respond. Each muscle has 

 motor neurones which act as selective 

 transmitters. This is the explanation 

 (Weiss, 1936: Biol. Rev. 2:464) for the 

 simultaneous movement of homologous 

 muscles even though transplanted limbs 

 may be supplied by non-homologous nerves. 

 (See function, homologous. ) 



RESPONSE, HOMOLOGOUS - an extra (trans- 

 planted) muscle is made to act by the cen- 

 tral nervous system together with the nor- 

 mal muscle of the same name. 



REUNITION - reassembling of parts of an or- 

 ganism into a functional whole (e. g. , sponges 

 as Microciona) after separation of compon- 

 ent parts. 



RICHTUNGSPOLARITAT - (German) polarity of 

 direction, orientation of particles toward 

 the animal or the vegetal pole, but found 

 throughout the ovum. 



ROHON-BEARD CELLS - giant ganglion cells in 



the spinal cord, derived from the trunk neural 

 folds, and which fornn the sensory pathway 

 including that of the peripheral sensory nerves. 

 They have large rounded nuclei and a consid- 

 erable amount of cytoplasm which stains dif- 

 ferentially with Heidenhain's modification of 

 Mallory. They are never found in the ven- 

 tral part of the cord. They are associated 

 with that sensory area which is functional 

 during the flexure of the tail following tactile 

 stimulation. 



RHYTHM, METACHRONAL - sequential contrac- 

 tion (cilia or muscle). 



RHYTHM, SYNCHRONAL - simultaneous contrac- 

 tion (cilia or muscle). 



SECTION CROSS - cut made at right angles to 

 the long axis of the embryo. Syn. , trans- 

 verse section. 



SECTION, FRONTAL - cut made parallel to the 

 longitudinal axis of the embryo and separat- 

 ing the more dorsal from the more ventral. 

 Syn. , horizontal section. 



SECTION, SAGITTAL - cut made parallel to the 

 longitudinal axis of the embryo but separating 

 the right from the left portions. Term often 

 confused with "median" or "longitudinal" 

 which really mean no more than "axial, " 

 hence could also be "frontal". 



SECTIONS, SERIAL - thin (microscopic) slices 

 of an embryo laid on the slide in sequence 

 (generally from left to right, as one reads) 

 so that the beginning of the embryo is at one 

 side (left) and the end of the embryo at the 

 opposite side (right) of the slide. 



SEGMENTATION - term used synonymously with 

 cleavage. Also means serial repetition of 

 embryonic rudiments (structural patterns) 

 in successive levels of regular spacing, as 

 in the case of somites, and spinal nerves. 

 Syn. , cleavage. 



SEGREGATION - the separation of self-differ- 

 entiating embryonic rudiments; the organ- 

 izational process of embryogeny; autonom- 

 izing (Weiss); the aggregation of various 

 spatial systems independent of each other 

 and leading to self-differentiating potenti- 

 alities. Originally used (Ray Lankaster) in 

 discussing the gastrea theory to mean a 

 separation of the physiological molecules that 

 are going to form ecto- and endoderm. 



SEGREGATION, EMBRYONIC - progressive re- 

 striction of original potencies in the embryo; 

 the process of step by step repartitioning of 

 the originally homogeneous zygote into the 

 separate parts of the presumptive embryo. 



SEGREGATION, PRECOCIOUS - segregation 



found in mosaic eggs where local differences 

 arise even before cleavage and a minimum 

 of modification in response to any internal 

 environmental factors occurs in subsequent 

 development (Lankester, 1877). 



