6 AUGUSTA ÄRNBÄCK-CHRISTIE-LINDE, NORTHERN AND ARCTIC INVERTEBRATES. 



This view enunciated by Herdman, viz. that protogyny occurs in the Botryllidce, 

 lias been also adopted by Miciiaelsen \ for he states that »die Personen im jugend- 

 lichen Zustand rein weiblich, im ältesten Zustand rein männlich erscheinen. Soweit 

 ich die Angaben iiber Geschlechtsverhältnisse bei Botrylliden iibersehe, ist dies das 

 allgemeine Verbalten in dieser Familie» (1. c. p. 110). As to Metrocarpa (Botryllus) 

 leachi, which was subjected to a special investigation låter (1921), Michaelsen ex- 

 presses the view that »Die Personen des B. leachi sind wenigstens zumeist protogyn 

 zwittrig, vielleicht zum Teil eingeschlechtlich männlich. — — - Hoden sind an 

 diesen Knospen nicht erkennbar, sie sind noch rein weiblich» (1. c. p. 105). Thus 

 Michaelsen's view is that the usual arrangement in the Botryllidce is for the male 

 and female organs to appear at different stages so that in young individuals only female 

 organs are present, and in full-grown individuals only male organs. Just the contrary 

 of that, however, has been proved to be the case above; the rudiments of testis present 

 in the young buds were evidently overlooked. The expression »protogyn zwittrig • is not 

 moreover to be understood as implying that the ova are mature before the sperma- 

 tozoa, for sections of young zooids show the presence of both ova and spermatozoa 

 well developed. 



Stage II (Pl. 1, fig. 1). The young zooid which represents the second stage 

 measures about 1 mm. in length; it has not attained its full development. The stalk 

 connecting it with the parent animal is fairly long; the siphons are but little developed, 

 but apart from that the young individual shows all the typical features, especially 

 in regard to the reproductive apparatus, the structure of which is easily distinguished 

 and noticeable. As appears from the figure the male and female organs are well 

 developed ; they are found on both sides of the body. The ovary is situated at the 

 posterior end of the body, the testis lies directly in front of it. Both organs are 

 large rounded masses, projecting from the body-wall, the testes from the sides of the 

 body and the ovaries from the posterior end, which gives to the animal a somewhat 

 peculiar outline. 



The male organs consist of a single testicular gland on each side of the body. 

 The two testes are not always on a level with each other. In the zooid described, 

 the testis on the right side is situated farther back than is that on the left. Each 

 is a rounded, lobate body, somewhat compressed from either side. The lobes are 

 large and, in this individual, five in number. The sperm-duct is verv short, pro- 

 jecting from the middle of the inner side of the testis and opening into the peri- 

 branchial cavity. 



The ovaries are enclosed in diverticula of the body-wall, that project from the 

 posterior end on each side of the body. Those diverticula are dilatations of the 

 mantle and do not represent well marked-off sacs. As in the stage above described, 

 the female organs are represented by a group of eggs on each side, one of which is 

 greatly distended in size but the others are very small. Only one large egg has been 

 observed to be present at one stage on each side of the body. Often there is a large egg 



1 Michaelsen, W., Ascidia Ptychobranchia und Diktyobranchia des Koten Meeres. Denkschr. K. Akad. 

 d. Wiss. in Wien. Bd. 95. Wien 1918. 





