286 NATHAN FASTEN. 



SUMMARY. 



1. During the latter part of June and early portion of July the 

 testis of Lophopanopeus bellus (Stimpson) Rathbun is in the best 

 condition for the study of the spermatogenesis process. 



2. Primary and secondary spermatogonial divisions can be 

 distinguished. The spermatogonial chromosomes are univalent 

 and probably number around 124. 



3. Large nutritive cells are frequently associated with sperma- 

 togonial strips in tubules where there are mature spermatozoa. 

 These have irregular nuclei, and are, undoubtedly, produced 

 from primary spermatogonia which have failed to mature. 



4. The primary spermatocyte undergoes growth, parasynapsis, 

 tetrad-formation and reduction division. There are 62 bivalent 

 chromosomes seen in polar views of the metaphase stages of this 

 division. 



5. During the growth period a chromatoid body appears in the 

 cytoplasm, and when the reduction division takes place this 

 wanders undivided to one of the poles of the cell, resulting in the 

 formation of two kinds of secondary spermatocytes, one which 

 possesses the structure and the other which is devoid of it. 



6. There is no rest period between the primary and secondary 

 spermatocytes. The division of the latter is equational and 

 produces two types of spermatids, one having a chromatoid body 

 and the other which is minus such a structure. This last type 

 is about three times as numerous as the former one. 



7. At an early stage, the chromatoid body is expelled from the 

 spermatids which contain it, and from then on all the spermatids 

 undergo similar complicated transformations. These changes 

 bring about the formation of the radial spermatozoa which are 

 packed away in single spermatophores within the vas deferent 

 ducts. 



8. Four kinds of mature spermatozoa may be distinguished, 

 namely, three-, four-, five- and six-rayed types. The four- and 

 five-rayed spermatozoa are the ones which are encountered most 

 frequently. 



