104 



ACTINIARIA 



The mesenterial filaments are only present on the mesenteries of the first order. The ventral direc- 

 tive pairs are, however, devoid of ciUated streaks. Below the aboral prolongation of the siphonoglyphe the 

 filament namely begins as a weakly developed, single cnido-glandular streak of inconsiderable dimension, 

 gradually growing thicker and attaining its largest dimensions in the reproductive region. As in certain 

 Zoantharia (for instance Isozoanthus gigantcus) and in the Ceriantharia the ciliated streaks have probably 

 here fused with the aboral prolongation of the siphonoglyphe and the actinopharynx, though the different 

 parts of the filaments of the prolongation cannot be distinctly traced. Possibly the continuation of the sipho- 

 noglyphe and the recurvated part correspond to the ciliated streaks, the folded parts to the cnido-glandular 

 streak. The imperfect mesenteries are devoid of filaments. The ciliated streaks are of typical appearance. 



Only the mesenteries of the first cycle are fertile. The spe- 

 cies is dioecious. The ovae are provided with a covering, 

 decked by spines. 



L,arvae. (Synonymy and literature, compare Carl- 

 gren 1906, p. 81). 



The larvae of tliis species, living on several hydroid- 

 medusae, have been anatomically described before by my- 

 self and by several other authors, wherefore I do not give any 

 details of its anatomy here. The younger stadia with only 

 3 couples of mesenteries are disc-like (Carlgren 1906 fig. 

 6 a). Somewhat older stadia are a little more rounded, still 

 older ones are more elongated and acuminated in the aboral 

 end, only in the adult animal the body is cylindrical. The ex- 

 terior aspect of the larvae in different stadia I have shown 

 1906 (textfig. 6). On the plate i, figs. 21—29 I have completed the series (all larvae sketched on the samef 

 scale). The arrangement of the tentacles I have described before (1904). The first eight visible tentacles are 

 distinctly seen on fig. 25, PI. i. On fig. 26 b, PI. i two of the younger tentacles are conspicuous. In the older 

 larvae a three-lobed conchula little by little appears, which I have been able to state by feeding larvae during 

 two months in an aquarium. A specimen dredged by myself on the clay (figs. 28, 29, PI. i) also had a three- 

 lobed conchula, but only 10 tentacles. This reduced number of tentacles is associated with an abnormal 

 development of the mesenteries (compare below!). The colour of the column of the older larvae was opaque- 

 white, the shades of colour pretty well agree with those of figure 5, PI. 17 in the work of Had do 11 and Dixon 

 (1885). Therefore I have no doubt at all that the larvae belong to Peachia hastata.With P. boeckii they cannot 

 be identical as the colour of P. boeckii is another, and this species also in other respects is different from P. 

 hastata. That only 3 lobes are developed in the larvae may be referred to the small size of the animals. Evi- 

 dently these three lobes correspond to the three main lobes of the adult P. hastata which later on, as the ani- 

 mal grows in size, develop a few or many secondary loljes. 



Concerning the appearance of the mesenteries, those of the 5tli and 6th couples seem to originate 

 in the typical places, so that the former form pairs with the dorso-lateral, the latter with the ventro-lateral 



Textfig. 134. Peachia hastata. 

 Transverse section of a yoniig anormal specimen. 



