GLOSSARY 



SEGREGATION. The separation of allelomorphic genes and their distribution into 

 separate cells during one of the meiotic divisions. CJ. DISJUNCTION. 



SELF-FERTILIZATION. Union of gametes produced by the same individual which may 

 occur in some hermaphroditic organisms. CJ. CROSS-FERTILIZATION. 



SEMINAL. Pertaining to or containing spermatozoa. 



SEMINIFEROUS TUBES. Tubes of the testis along the walls of which the spermatozoa 

 are dilTerentiated. 



SENSE ORGAN. A multicellular receptor; an organ containing cells especially sensi- 

 tive to some particular type of stimulus. 



SENSORY CELL. A unicellular receptor. 



SEPTUM {pi. SEPTA). A partition between two cavities. 



SEROLOGY. Study of blood serum; specifically, study of the immunity reactions 

 developed by mammals and revealed by their sera; particularlv useful in deter- 

 mining the apparent degrees of chemical interrelationship between the proteins 

 of different kinds of animals. 



SERUM. The liquid that separates from a blood clot; blood serum contains no cells 

 or fibrin. 



SESSILE. Attached; not free-swimming. CJ. SEDENTARY. 



SETA {pi. SETAE). A bristle. 



SEX. A characteristic condition of animals in which the individuals are either male 

 or female and are distinguished essentially by the production of spermatozoa or 

 ova, respectively. 



SEX CHROMOSOMES. Chromosomes that differ in number and distribution in the 

 males and females of a species; the X- and Y-chromosomes. CJ. AUTOSOMES. 



SEX-LINKED INHERITANCE. The inheritance of characters conditioned by genes car- 

 ried by the X-chromosomes. 



SEX-REVERSAL. The loss of original sex characters and the assumption of those of the 

 opposite sex. 



SEXUAL REPRODUCTION. Reproduction by union of gametes like those produced by 

 sexually differentiated individuals; this term is commonly used as a svnonvm for 

 reproduction by syngamy. CJ ASEXUAL REPRODUCTION. 



SEXUAL UNION. Temporary association of male and female organisms during which 

 sperm are introduced into the reproductive tract of the female. 



SILICEOUS. Containing or consisting of silica, which is characteristic of sand. 



SINUS {pi. SINUS or SINUSES). A cavity. 



SIPHON. A canal. 



SKELETON. The hard parts of an organism which serve to support and protect soft 

 parts. CJ. ENDOSKELETON and EXOSKELETON. 



SOCIAL. Living in groups. CJ. SOLITARY. 



SOL. A liquid state of protoplasm or any colloid. CJ. GEL. 



SOLENOCYTE. See PROTONEPHRIDIUM. 



SOLITARY. Living alone. CJ. SOCIAL. 



SOMATIC. Pertaining to the body of an organism. 



SOMATIC CELL. In colonial Protozoa, a cell that has lost the capacity of reproduction. 

 In Metazoa, a cell which may divide in the growth of the organism but which 

 is not directly involved in the reproductive activities of the individual. CJ. 

 GERM CELL. 



SOMITE. One of a series of homologous parts arranged in a row. Cf. SEGMENT 

 and MESODERMAL SOMITES. 



SPECIES {fil. SPECIES). A subdivision of a genus, sometimes separated into varieties. 



SPERM. See SPERMATOZOON. 



SPERMATOGENESIS. Ihe difTerentiation of the spermatozoa. CJ. OOGENESIS^ 



SPERMATOZOON {pi. SPERMATOZOA). A mature or differentiated male germ cell; .a 

 microgamete. Cf. OVUM. 



675 



