90 Notes on the Ascidea Manhattensis, De Kay, 



its chorion. The orifice had ai^proached, on the 1st of August, 

 more or less, one apex ; in some specimens — which were now 

 oval — it was terminal. 



In my notes taken at the time (1851), no doubt is expressed 

 as to the identity observed soon after they were ejected, and 

 examined for three successive days, and those observed subse- 

 quently, until a central orifice was formed containing one em- 

 bryo. — (Of the microscopical examination of the morphological 

 changes taking place inside, which led to no satisfactory results, 

 I refrain from giving any details). Having established the fact 

 that the Ilammarim are nurses, it is certain that a chansce of 

 generation takes place with the Molgulce. That there is such 

 an occurrence in nature as a change of generation was dis- 

 covered by Chamisso,* viz., with the SalpcB. His observations 

 in regard to this subject were considered for years as contrary 

 to the laws of nature, but were proved to be true and intro- 

 duced into science by Steenstrnp,t who deduced from them, 

 and from analogous observations among the lower animals, laws 

 now generally' recognized. 



In 185Y I found the calices of the ovaries filled with mature 

 ova on the 12th of August, and on tlie 23d of the same month 

 3'oung MammaricB, where I had found them before, viz., on 

 the mantle at the base of the tubes — with reference to the time 

 of their development — two days earlier than in 1851, a differ- 

 ence accounted for by the temperature of the respective years. 



I have delayed the publication of the results of my investiga- 

 tions, desiring again to study minutely, and at short intervals, 

 the ova from the time of ejection to that of the formation of the 

 embryo, but have had no opportunity of doing so. 



* De animalibus quibusdam e classe vermicem Linasana. Fascic. I. de Salpa 

 Berolini 1819. 



f Ueber den Generationswechsel oder die Fortpflauzung und Entwicklung 

 durch abwechsehide Generationen, eine eigenthiimliche Form der Brutpflege 

 in den niederen Thierklassen. Kopenhagen 1842. 



