46 



longitudinal incision was made through this substance, and it was 

 found after cutting about one-eighth of an inch inward, that the 

 knif centered a cavity from which fluid was driven out with some 

 force. On examination, it was found that this cavity was lined 

 with a rather tough membrane not unlike the external coat, 

 except that it was much smoother, and no openings could be 

 found in it. I was not prepared for this cavity, and it was 

 too late to take careful measures to ascertain whether it com- 

 municated by any canal with any other part of the structure, 

 but a prolonged search with a fine probe did not reveal any 

 fsuch opening, and I am inclined to believe that the only com- 

 munication between the walls of this cavity and the other 

 portions is by imbibition through the substance of the structure 

 itself. 



During the dissection it was abundantly shown that the 

 chief mode of growth, if not the only one, in this compound 

 form was budding. I met with numerous buds growing inward 

 from the lower part of the more mature Ascidians, and also 

 embryo forms in all stages of development. We are all aware 

 that a mass of evidence has been accumulated within the last 

 few years tending to show that the Ascidian is the connecting 

 link in the stage of evolution between the invertebrata and the 

 vertebrata. The young larva of the solitary Ascidian has a 

 tail, but as in the case of the young embryo of man, the tail 

 disappears in the progress of development. Within this tail 

 there is a prolongation of nervous structures, which also dis- 

 appear, but during the existence of these structures the young 

 Ascidian has a close resemblance to the forms of animals on 

 the border land of vertebrata, as seen in the Amphioxus, one of 

 the primitive forms of fish. I have here specimens of embryos 

 dissected out from the substance of the Ascidian I am describ- 

 ing ; some are stained and others are simply mounted in pre- 

 servative fluid. All these show that even in the compound 

 Ascidians the embryos, though never likely to require to swim 

 about, but always confined in the substance of the tissue, within 

 which they are developed, have long well-formed tails, and in 

 some of the better marked specimens there is evidence that 

 there is within the tail a canal in which cells of a somewhat 

 ovate shape can be distinguished. These tails show under a 

 one-fifth objective unmistakable transverse m.arkings like those 

 of striated muscle. In one of the thicker specimens there are 

 numerous embryos, showing the stages of tail formation. Fig. 3 

 gives a view of one of these embryos, and c shows the fully 

 formed tail winding around the body. 



It will be remembered that in the embryo of the solitary 

 Ascidian, and in its early free swimming stage of existence, 

 there is to be seen near the head three rope-like appendages, 



