10 AUGUSTA ÄRNBÄCK-CHRJSTIE-LINDE, NORTHERN AND ARCTIC INVERTEBRATES. 



ovarial cells is due to a mistake as has been proved above; its formation from the peri- 

 branchial sac has evidently been overlooked. Nor does it seem probable that ovarial 

 cells could be used as nourishment for the embryo; at least, as far as I can see, 

 nothing has been stated to support such a view. The question as to whether more than 

 one emb^o on each side is produced in Metrocarpa, cannot be answered without further 

 investigations. In coming to a decision on the question, the following facts will have 

 to be considered: 



a) In the very young bud the female organs consist of numerous eggs or, in 

 conformity with the terminology used above, they consist of numerous rudimentary 

 ovaries. 



b) Large eggs have been found in young individuals (ef. stage II) and in full- 

 grown individuals too. 



c) Small eggs have been observed in zooids that have embryos in the brood- 

 pouches and as to their development we know nothing for certain as yet. 



In the description of the new Botrvllid species, Botrylloides parvulum Huitfeldt- 

 Kaas, from the Norwegian coast, there is a figure given representing two young zooids 

 furnished with well developed brood-pouches. The species described by Huitfeldt- 

 Kaas j is no doubt to be referred to the genus Metrocarpa. But the true character 

 of the brood-pouches that are shown on the drawing (1. c. Pl. 2, fig. 29) has escaped 

 the observation of the investigator. No attention has been paid to those organs in 

 the description he gives, for the only statement referable to them is as follows: 

 »the o va and larv se are of an orange yellow colour, and unusually large» (1. c. p. 24). 



Stage V (Pl. 1. fig. 4). In the stage which is to be described the zooid is 

 of larger size than in stage IV; it measures about 2.5 mm. in length. The testes 

 are still well developed, but as compared with those in the individual examined 

 above they appear somewhat reduced in size: the lobes are less voluminous and 

 less swollen. In this individual too the testis on the right side is situated farther 

 back towards the posterior end than is the one on the left side. 



In studying the figure illustrating this stage one is, however, above all struck 

 by the development of the brood-pouches. They are in the form of large, globular 

 sacs, enclosed in wide dilatations of the body-wall and projecting into the common test. 

 They each contain one embryo, which has almost attained the fully developed Ap- 

 pendicularia-stage. In those pouches the embryos undergo their full development 

 and, judging from the conditions found in this stage, they do not pass out of them 

 until they are completely developed tailed larvse. 



In the common cloaca tailed larvse have often been found. Moreover, empty 

 brood-pouches showing no rupture have sometimes been observed. Those facts seem 

 to favour the supposition that the larvce, having attained their full development in 

 the brood-pouches, enter into the peribranchial cavity, from where they pass into 

 the common cloaca. 



The zooids examined belong to colonies caught during the month of July. 

 Colonies in stage V were collected at the end of that month. Colonies collected 



1 Huitfei.dt-Kaas, H., Synascidiie. The Norwegian North Atlantic Expedition 1876 — 187tf. Cliristiania 1890. 



