SECONDARY SEXUAL CHARACTERS OF CRAYFISHES. 233 



It seems likely that the survey need only be extended to discover 

 many more specimens since the present ones were taken in a very 

 limited bit of collecting. 



DESCRIPTION OF SPECIMI \-. 

 i. Specimens of Cambarns 'drills. 



T\\o -pe< miens have been taken from the tributarily of the 

 Rock Kivrr in the vicinity of Beloit, \Yi-ron-in, both bearing in 

 a<lilitir)ii to the COpulatory hooks of thf third ualking lei;s > 

 nd pair of such hooks on the seeond walking legs. The 

 adiliiinii.il hook- were slightly smaller than the normal <>m> Inn 

 \\ere distinct. Both specimens were about t\\o \eai> old. 

 They represented a proportion of about .5 |HT eeiit. <>f all the 

 male- taken. 



A i olid linn of large specimens examined at thr 1 ni\et-ity oi 

 \Yi-rn-in .UK! later traced through a supply t oinpany to north- 

 ea-iei ti \\ 1-1 onsin as the locality from which tin- rolUviion ( .mu- 

 < niii.iinrd forty-c'ight males of which sixtrni had copul.itor\ 

 hiink^ upon the second walking legs in acldiii"n ID iliD- t D| ilu- 

 third \\alking legs. Two other males in this >.mir rullrriion had 

 M< li a -in-Jr additional hook upon the K-M -TDMI| \\.tlkinu K-v;. 

 Thr additional hooks were in some cases as \\i-ll d-\flo|n-d ,i> 

 t In >-r in 'i m. illy occurring upon the third walking 1< -- I -in in m< s1 

 in-iaiiti- they were smaller. In this same lot of specimens tl 

 \\rit 3.5 |K-r cent, of females which posses^ -d rach a \\i-ll-(N-iiin-d 

 mak- li.irarti-ristic in the form of a pair of copulatory hook- on 

 tlu- third \\alking legs. 



2. L'iunbarus propinqims. 



In ilii- -prrir- the occurrence of males with additional male 

 characteristics has been found to be rather con>tant but in no 

 locality ha- there been so large a proportion of aberrant indi\ id- 

 nal>a- in (\inilxirnsvirilis. There is, howe\er,a greater variation 

 in the additional characters. In some instances the additional 

 hook- are found upon the fourth walking le-- and in other- 

 upon the -((.Mid \\alking legs. 



During the -iimnier of 1922 considerable numbers were 

 collected from time to time from Turtle Creek but only two 

 mali> were notiied \\hich had extra copulatory hook-. In one 



