614 GEOLOGICAL SURVEY OF THE TEEEITOEIES. 



appendages, sometimes branched, as in StreptocepJialus (Fig. 13), while 

 in the female they are simple and end in a mucronate point. In Apus, 

 the sexual differences consist in the rounded egg-sacs ot the female on 

 the eleventh feet ; in the family of which Limnadia is the type, the first 

 pair of swimming-feet in the male end in large, clumsy hooks, adapted 

 as clasping-organs. 



Now, besides the ordinary, normal mode of reproduction, several 

 genera of the phyllopods are known to reproduce by what is termed by 

 Professor Owen parthenogenesis^ or virgin reproduction ; i. e., the eggs 

 arise from the ovary by a budding process, like the budding of leaves 

 on a tree, through the simple multiplication of cells, without fertiliza- 

 tion by the male spermatic cell. This occurs in several insects, as in 

 the Aphis, the honey-bee, the silk-moth, «&c., and in Daphnia, the water- 

 flea, which is closely allied to Sida (Fig. 1), and in other Untomostraca, 



A Russian naturalist, Schraankiewitsch, in 1872, discovered a variety 

 of " Branchipus " {Arteniia) Arietinus, near Odessa. In the summer 

 and autumn of the year before, he noticed that this Artemia changed its 

 form, corresponding to the greater or less saltness of the water. In sum- 

 mer, when the water was most salt, there was a retardation in growth ; 

 and this retardation was the more evident the higher the temperature 

 and the more concentrated the solution of salt. Toward the end of the 

 summer, when heavy rains set in and the temperature decreases, the 

 Artemia becomes larger, loses its red and gray color, and becomes clear 

 and transparent, so that the July generation has important differences 

 from that which appears in November. In order to observe this phe- 

 nomenon carefully, he undertook the artificial breeding of the Artemia 

 in two different ways. In one vessel, he increased the saltness of the 

 water up to 18° Baume ; in another, he reduced the solution to 3°, and 

 thus reared several generations. In both cases, he remarked that each 

 new generation easily lived in such a concentrated solution as the pre- 

 vious generation could scarcely live in. By raising them in so different 

 solutions (18° and 3° Baume), very differerent forms of Artemia were 

 obtained, which were not to be found in their original pond. 



" While carrying on these observations, he at the same time proved 

 that a parthenogenetic reproduction exists in Artemia. Each time, both 

 in the great increase of the weak solution as well as in the greatly 

 increased saltness of the water, the females produced new generations, 

 despite the absence of the males. Under these relations of the solu- 

 tions, in warm weather, only females were produced. These females 

 produced in similar breeding-jars only female offspring. Only in water 

 of medium strength were produced males." 



As a further illustration of the influence of physico-chemical surround- 

 ings on the organization of these animals I will again quote from the 

 abstract of the remarks of our author. '' In the salt-pools in the neigh- 

 borhood of Limaus (near Odessa), he found in the spring, together with 

 Branchipus {Artemia) ferox, Gr., a very jyeauMar Artemia, which he thought 

 was undescribed. He thought from certain characters that this species 

 belonged to the higher group of Branchipus. In this form, he observed 

 some strange differences in the structure of the sexual organs, changes 

 which could scarcely be regarded as pathological. Usually, the horns 

 (lower anteunse) of the females are small, but in the old females they are 

 clearly elongated, and are very much like the claspers of the males. Still 

 earlier appears a striking change in the structure of the genital organs, 

 when in some, characteristics of the male organs appear. In like man- 

 ner, the sexual organs are clearly changed in the old males ; and, in the 

 sacs in which the outer sexual organs lie, we find a space which is very 



