288 A. T. MASTERMAN. 



To these we must add that Cobbold (4) describes, ia 1857, 

 the occurrence of Actinotrocha in the Frith of Forth. His 

 paper is principally notable for the statement that the larvae 

 fixed themselves by their anal extremity. 



Two years after (1859), Dyster (8) noted the eggs and early 

 stages of Phoronis. We may add that in 1888 Mcintosh (15) 

 gave, in connection with his anatomical account of Phoronis 

 buskii, two figures and a short description of some early 

 stages of Actinotrocha from the tentacles of the adult. 



We may only add to this short account the fact that 

 Actinotrocha, after it was once proved to be the larval form 

 of Phoronis, has in various text-books and general zoological 

 articles been usually interpreted as a much " modified trocho- 

 sphere'^ larva, whilst comparisons have been drawn between 

 its structure and that of the Echinoderm larvae. Although 

 several authors, to be mentioned later, have drawn a com- 

 parison between the adult Phoronis and the Hemichordata, 

 Harmer (10) is the only author, as far as I have been able to 

 ascertain, who has attempted a tentative comparison between 

 the organs of Actinotrocha and those of Balanoglossus. 

 His deductions were limited in extent, owing to the supposed 

 absence of the notochord, gill- slits, and mesenteries separat- 

 ing the cavity of the pre-oral lobe from those of the lopho- 

 phoral region. 



External Form. 



The species of Actinotrocha referred to in this paper 

 does not appear to differ in any essential respect from that 

 originally described by J. Miiller near Heligoland, and named 

 by him Actinotrocha branchiata. The specimens here 

 figured were caught by the bottom tow-net in St. Andrews 

 Bay. In the absence of knowledge with respect to the adult 

 in both cases the minor difference need not concern us here. 

 Although the general appearance of Actinotrocha is familiar 

 to every zoologist from the figures of Miiller (16), Wagener 

 (20), Metschnikoff (14), and many others, copied more or less 

 accurately into nearly every illustrated text-book, yet I have 



