4 



MARINE AND FISHERIES 



6-7 EDWARD VII., A. 1907 



GYMNODINIID^. 



PYROOYSTis. — Murray. 



'J'his genus was established by Sir John Murray for certain globular cells met with 

 ir the tropical and subtropical portions of the ocean, which are frequently responsible 

 for the phosphorescence of the sea. The species met with, P. noctiluca (of large size, 

 viz. : 600 — 800 in transverse diameter) was accompanied by a spindle-shaped form 

 P. fusiformis Murray, measuring 1,000 x 160/x. Also at Canso a globular form of 

 smaller dimensions (80 x 150/x) was frequent (Plate I., fig. 3), agreeing admirably 

 in the nature of the protoplasmic contents with P. noctiluca. It was also accompanied 

 by a crescentic form (Plate I., fig. 5) 180 — 250 /a in length by 18 — 25,a greatest 

 width which has been frequently found in the north Atlantic, and described by 

 Schiitt as P. lunula. The association soon turned out not to be fortuitous, for all 

 stages of segmentation of the protoplasmic contents of the globe into 4, 8, 16, 32 balls 

 were observed (Plate I., fig. 4), which eventually developed into crescents within the 

 shell of the globe before they were freed by the bursting thereof. The curiously curved 

 shapes which they acquire during their imprisonment are explained by their crowded 

 arrangement. A further phase of development, in virtue of which six Gymnodinia 

 (fig. 5, 5a) are formed within the crescent (one of which is distinguished from the 

 others by a red spot), was observed such as is figured by Hensen (No. 1, Plate IV., fig. 

 30) . Schiitt figures examples with only a single Gymnodinium in the interior. It seems 

 improbable that only one species of Gymnodinium passes through this remarkable 

 cycle, and further studies may reveal globular and fusiform cystic stages for other 

 species. Another cyst occurring along with the foregoing, but exceeding it in size 

 (diameter 200 — 250;^) is probably related. It was observed frequently with daughter- 

 cells sixteen in number of characteristic form (Plate I., fig. 6) and size (50 — 56 /^.), 

 one alone of which possessed a rosy spot. The cells afterwards undergo encystment 

 when, within each, eight granddaughter cells of similar but smaller size, 12//, are 

 develoi3ed, one only of them retaining the original rosy spot. 



In July and August there was frequently observed within dead Copepods or their 

 appendages, a small pink Gymnodinium (Plate I., fig. 7) of subgfobular form, 40// in 

 its longer diameter, generally in an encysted condition, the nuclei recalling the struc- 

 ture figured by Schiitt (No. 2, Plate XXII., fig. 73). It is probably a stage in the 

 development of a larger form. 



POUCHETiA — Schutt, 



This genus has been formed by Schiitt for the purpose of separating certain 

 chlorophylless species of Gymnodinium which are also distingiiished, alone among 

 marine forms, by the possession of more or less complicated organs of vision. 



About the midde of July at Canso a form was common which possessed the 

 yellow and brown chlorophyll of Schiitt's Gymnodinium geminatumi, disposed in 

 strands, but in addition a well marked pigment spot with lens of the form represented 

 in Plate I., fig. 8. As this is manifestly of the same character as the stigma of the 

 other species of Pouchetia, that genus must be held to include also chlorophyll- 

 bearing forms. The present species, which on account of its colour may be called 

 P. ochrea, was always observed encysted, ^ single individual or one in various stages 

 of division being inclosed in the cyst. The latter envelopes the body closely, and is 

 not the thick gelatinous investment seen in 6^. geminatum. The undivided cell 

 measures 55 x 45/^ but when division is far advanced it gains a length of 100/a. 

 The form and position of the lens and pigment body of the stigma may be gathered 

 from the figure. The latter shows that the two daughter individuals, instead of 

 being in contact by similar surfaces, have their opposite poles adjoining. 



