and on the Mmnmaria Manhattensis. 87 



become firmly united before the withering away of their appen- 

 dages," as well as other facts, support that supposition. 



The development of the Mammaria continues after the lar- 

 va has escaped. Their aggregation in the common envelope 

 in circular or oval form resembles that of the compound As- 

 cidians. The common envelope increases in size, already ob- 

 served by Milne Edwards in reference to the compound Ascid- 

 ians ; it contains, as I ascertained, elastic fibres (muscles), 

 which contract independently of the contractions of the Mam- 

 marice. Later in the season it assumes difierent forms ; is 

 gradually detached from the objects to wdiich it adhered, and 

 is then (September and October) carried away by the waves. 

 The Mammfiarim to which Lamarck refers were found floating; in 

 the water. 



Within the common envelope gemmation takes place. 



Having proved that the Ifammaria observed by me is a. 

 nurse, I believe I can safely conclude that all Mammarioe, are 

 nurses, and it follows that they cannot be classified with the 

 Ascidians as a subfamily. 



In regard to the question to which parent animal the Mam- 

 maria under consideration stands in a genetic relation, I made 

 some investigations during the following summer, 1851. 



As I had found them on the mantles of the Molgula Maii- 

 hattensis, after the ova were ejected, I inferred that its ova 

 possibly might be metamorphosed into 3fammari(B, being con- 

 vinced already from previous studies respecting the structure of 

 the cloaca, which represents a short tubular canal into wdiich 

 the vas deferens opens between the orifices of the (2) oviducts, 

 as well as the development of the ovaries, etc., that the ova 

 would be fecundated during their passage through the cloaca, 

 and developed outside of the parent animal. Accordingly, when 

 I observed that the ovaries of numerous animals wei'e filled 

 with mature eggs, — the germinative follicles (Keimschlauche) 

 having disappeared, with the exception of comparatively few 

 situated on the dorsal and ventral sides of the ovaries, their 



