S ta t i s t i ca l data . I n t e r ac t i ng galaxies inc lude ga l axies with d i s to r t ed shape, ga laxies i m m e r s e d in a common luminous cloud, coa lesc ing galaxies , ga laxies joined by a bar and showing " ta i l s , " c lose groups ("nes t s" ) , and chains of ga lax ies . It is quite c lea r that these objects differ in their na tu r e . Thus, in c lose sys t ems of ga lax ies the re mus t be t idal forces (d i s to r t ion of shape and broad diffuse ba r s ) . On the other hand, n a r r o w and long tai ls and b a r s between ga laxies c a n i not be due to t idal i n t e r ac t i ons . I n t e r ac t i ng gaIaxieS a r e not at a l l r a r e except ions . In the morpholog ica l Catalog of ga laxies [1-4] , which conta ins desc r ip t ions of about 29 000 objects, there a re about 1760 s y s t e m s of i n t e rac t ing ga laxies or s y s tems that a r e suspec tpd to be of this type. They i n clude about 2250 ga lax ies d e s c r i b e d in the catalog. Thus, one in t e r ac t ing iga l axy is found, on the average , for every 16-17 s inglb galaxies , and one i n t e r ac t i ng galaxy for every 12-~3 o r d i n a r y ga lax ies . Although I the l imi t ing s t e l l a r magni tude for the i n t e r ac t i ng gal axies in the catalog is I somewhat g r e a t e r than for the r e m a i n i n g ga laxies , this has no apprec iab le effect on these r a t io s s ince the inumber of ve ry weak i n t e r a c t ing ga laxies de sc r i bed in the catalog is sma l l . F i g u r e 1 shows th@ obse rved n u m b e r of i n t e r a c t i ng s y s t e m s per unit solid angle as a function of the photographic s t e l l a r magni tude of the b r igh tes t m e m b e r of the sy s t em. The e s t ima ted s t e l l a r magni tudes given in Vol. 1 of the morpholog ica l catalog [1] may be subjec t to s y s t e m a t i c e r r p r s [4] (the d i s t r ibu t ion of the i n t e r ac t i ng s y s t e m s over the s t e l l a r magni tudes conf i r ms this) . The c r o s s e s in Fig . 1 show the r e l a t i on ship based on data in the las t th ree vo lumes of the catalog. The s t r a igh t l ine co r re sponds to an equal dens i ty of i n t e r ac t i ng sy s t e ms at a l l d i s t ances . It follows f rom Fig . 1 that approx imate ly one s y s t e m of i n t e r ac t i ng ga laxies inc luding n u m b e r s b r i gh t e r than 11 m occurs per s t e r ad i an . A s s u m i n g that the mean absolu te s t e l l a r magni tude of the b r igh t e s t galaxy in the s y s t e m is -19 .5 , we find that the mean d is tance between the i n t e r ac t i ng s y s t e m s is about 10 Mpc. Let us cons ide r the spa t ia l dens i ty of the i n t e r ac t ing ga lax ies as a funct ion of the densi ty of n o r m a l ga l axles (in c lu s t e r s ) . The r e s u l t s of the ana lys i s based l a rge ly on the morphologicaI catalog a re given in Table 2 on p. 177. The f i r s t co lumn of Tab le 2 gives the coord ina tes of the c l u s t e r s and their abbrev ia ted des igna t ions . Next, an ind ica t ion is g iven of the p redomina t ing type of galaxy in the c lus te r , and the n u m b e r of ga laxies in the c l u s t e r among which the in t e rac t ing galaxies were looked for . F o r all the d u s t e r s , with the exception of two, the n u m b e r N r e f e r s to a c lu s t e r of galaxies d e s c r i b e d in the morpholog ica l catalog. In the d i s tan t c l u s t e r s Cr B and UMa I the n u m b e r of ga laxies was d e t e r m i n e d d i r ec t ly f rom the P a l o m a r photographs. The fourth co lumn gives the n u m b e r N i of in t e rac t ing s y s t e m s (not the individual ga l ax i e s : ) .