78 CALIFORNIA ACADEMY OF SCIENCES. 



are cells of the first variety breaking- to pieces; they are 

 worn-out blood cells. Several stages in the process are 

 represented in the figures referred to. In 35, the gran- 

 ules are for the most part confined to a single layer on 

 the surface of the cells ; many cases can be seen in which 

 they are found exclusively thus disposed. In such cells 

 the nucleus is still intact and distinct. The other figures 

 taken in order explain the various stages of disintegration 

 as I suppose it to take place. The nucleus is the last 

 portion of the cell to disappear. Man}- of the detached 

 fragments are found in some specimens scattered among 

 the cells in the blood. 



I have no convincing evidence concerning the relations 

 existinix between the other varieties. 



Since my manuscript passed into the printer's hands, 

 Seeliger's recent paper ('93) on the origin of the " ex- 

 ternal mantle " of tunicates has reached me. This au- 

 thor, instigated by the observations of Kowalevsky, has 

 reviewed the question of the origin of the cells of the 

 test with the result that Kowalevskv"s conclusions are 

 fully confirmed, excepting in x^ppendicularia. In this 

 latter group (Oikopleura cophocerca was the species 

 studied) the author finds that ectodermal cells pass into 

 the substance of the " haus,"' while no mesodermal cells 

 were observed to do so. 



The other species studied by Seeliger were Salpa 

 democratica and Claveilina lepadiformis. In both of these 

 the migrating mesodermal cells are abundantly described 

 and illustrated, and the ectodermal cells were not found 

 to participate in the process. 



The protoplasmic processes of the ectodermal cells 

 projecting into the hyaline matrix of the test are also de- 

 cribed, and the author regards them as " Sekretfiiden," 

 thus agreeing entirely, as he says, with Salensky as to^ 

 their significance. 



