1875.] 199 [Brooks. 



We cannot fail to notice the connection between the manner in 

 which the male salpa is produced, and the numerous cases, through 

 the various groups of the animal kingdom, in which the male is, to 

 some extent, parasitic upon, or supplemental to, the female. 



The Cirrhipeds, Arachnids and the Argonaut, will at once suggest 

 themselves, as familiar instances of the occurrence of such a relation 

 between the sexes. 



These interesting theoretical points are simply mentioned here, as a 

 more exhaustive discussion of them is reserved for another place. 



EXPLANATION OF PLATE I. 



The small letters have the same signification throughout. 



a. "Wall of branchial sac. 



b. Wall of outer tunic. 



c. Sinus cavity. 



d. Branchial cavity. 



e. Egg. 



/. Opening of inner chamber of placenta. 



g. Cavity of inner chamber of placenta. 



h. Cavity of outer chamber of placenta. 



i. Branchial aperture. 



7c. Atrial aperture. 



I. Cavity of atrial chamber. 



m. Muscles. 



n. Ganglion. 



o. Nucleus. 



p. (Esophagus. 



s. Stomach. 



t. Intestine. 



u. Eheoblast. 



v. Pericardium. 



w. Inner tube of Stolon. 



x. Ovary. 



Figure I. Egg within the sinus system, and attached by a gubernaculum to 

 wall of branchial sac, within the cavity of which a few spermatic filaments are 

 seen. 



Figures II, III, IV and V. Successive stages of segmentation. 



Figure VI. Gastrula within the brood-sac. 



Figure VII. Embryo, soon after the primitive digestive cavity has become di- 

 vided into the branchial and placental chambers. 



Figure VIII. Embryo considerably advanced, showing the mid-atrium, I, and 

 one of the lateral atria, m, which has already begun to split and form the mnscles. 



Figure IX. Embryo at about the time that the stolon appears. 



Figure X. Stolon, at a very early stage, showing the ovaries, x, x ; [in this figure 

 the letters a and b were accidentally transposed, so that b represents the outer 

 tunic, and a, the branchial sac]. 



