STATE GEOLOGIST. 167 



however, two spots which are evidently devoted to special sense: 

 first, the processes on the fourth joint of the antenna?, which may 

 be siraply the seats of tactile sense, or may have nerves suitable for 

 perceiving chemical stimuli; second, the area on the forehead bord- 

 ered by a raised line and covered with little pits, each with a small 

 bristle. The character of this organ can be but conjectured; it may 

 be homologized with the frontal nervous organs of the Cladocera. 



The sexual organs are quite extensively developed, and periodical- 

 ly obscure the remaining viscera. In the male the simple testis is 

 situated in the second segment, and the single vas deferens after 

 numerous windings through nearly the entire length of the body, 

 opens at the base of the first abdominal segment under a spined 

 plate. A part of the vas deferens is of a glandular character and 

 secretes an elongate tube, the spermatophore^ which serves to con- 

 tain the spermatozoids, and is fastened by the male at the opening 

 of the median pore of the female; on contact with the water this 

 tube, which is at first soft, contracts and presses the contents into 

 the opening of the female organs. So long is the vas deferens that 

 as many as three spermatophores are sometimes seen in the body 

 at once. The spermatozoids are very small. The geniculated male 

 antennae are used in grasping the setae on the tail of the female, 

 and the curiously modified inner branch of the third foot of the 

 male may assist in fastening the spermatophore upon her body. 

 The ovary occupies the same position as the testes, and the two 

 ducts are coiled in the body from end to end, opening in the median 

 pore behind the fifth pair of feet. When the eggs are ready to be 

 laid, they are forced out, carrying with them a film of the secretion 

 of the lower, glandular portion of the ducts, which is of a collodion- 

 like consistency, and which forms the enclosing sac. The young be- 

 come fully developed sexually before they assume their final form, 

 and it is not unusual to find ova-bearing females which are not only 

 much smaller than the parent, but with considerable differences 

 in the various organs. 



This sort of heterogenesis is not uncommon among lower Crusta- 

 cea, for the young may difi'er much from the mother till after they 

 have themselves produced young. 



Four species have been recognized in America, of which one is 

 certainly identical with a widely distributed European form, and a 

 second is probably identical with an English species. C. palustris, 

 Brady, seems to depart considerabl}^ from the norm of the genus 

 and may prove a type of a marine genus. No true Canthocamptus 

 is more than accidentally marine. 



