6 JOHNS HOPKINS UNIVERSITY MORPHOLOGICAL MONOGRAPHS. 



No one who has not seen these animals under favorable conditions 

 can form any conception of the amount of animal life which pure sea- 

 water is able to support ; and the salpae are able to multiply with great 

 rapidity, both sexually and asexually, in order to avail themselves quickly 

 of favorable conditions. 



Each species of salpa has two generations in its life-cycle, known as 

 the solitary generation and the aggregated generation. 



The solitary salpa is born from an egg which is carried within the 

 body of the aggregated salpa, whose blood nourishes the embryo during 

 its development by means of a nutritive placenta, Plate III, Fig. 4, and 

 Plate XXXV. 



The aggregated salpa3 are produced asexually from the body of the 

 solitary salpa. 



Plate II shows the solitary form of Salpa democratica, and Plate 

 XLIII, Fig. 1, shows the aggregated form of the same species. In Plate 

 I, the solitary form of Salpa pinnata is sho"wn in dorsal view in Fig. 5, 

 and in ventral view in Fig. 6. The aggregated community of the same 

 species is shown in Fig. 2, and one of the members of the community in 

 Fig. 3. Figs. 4 and 7 show the dorsal and ventral aspects of the solitary 

 form of Salpa chamissonis, and the aggregated cormus is shown in Plate 

 XLI, Fig. 9, and one of its members in Plate VIII, Fig. 6. The solitary 

 form of Salpa cordiformis is shown in Plate IV, Figs. 3 and 4, and a part 

 of a "chain" of the same species in Plate IV, Fig. 6. Plate IV, Fig. 7, 

 is the embryo of the solitary form of Salpa scutigera, and Plate IV, Fig. 

 1, part of its "chain," and so on. 



In most species each aggregated salpa carries only one egg, so that 

 the solitary generation consists of only one individual; but in all the 

 species the aggregated generation consists of many hundred individuals, 

 and there is reason to believe that it has no fixed limit, but that the 

 solitary salpa may continue to produce aggregated salpae for an indefinite 

 time and in unlimited numbers. 



The aggregated salpa3 are born in sets or cormi. In the chain-like 

 cormi the number of individuals is usually more than a hundred, but in 

 circular cormi it is very much smaller, and each cormus of Salpa pinnata, 

 Plate I, Fig. 2, contains only eight or nine. 



In a few species, each aggregated salpa contains more than one egg, 

 but the number is small, and seems to be fixed and constant for the 

 species. In Salpa cordiformis, for example, there are five eggs, and each 

 chain-salpa gives birth to five embryos, Plate III, Figs. 2 and 3, em. 

 Salpa hexagona, Plate X, Fig. 10, also produces five embryos. 



