364 DR W. CARMICHAEL M'lNTOSH ON THE STRUCTURE OF THE 



of more than one globule on these thread-like organisms, and the comparative 

 steadiness of the body of the spermatozoon, contrasted with the lashing of the 

 tail, might have raised a doubt in the mind of the distinguished foreign author. 

 The spermatozoa in Tetrastemma vermiculus (Plate VIII. fig. 12), though minute, 

 are amongst the most active of the group. These structures are slender at one 

 end, and slightly dilate towards the opposite, which is furnished with a very long 

 tail. Just in front of the posterior end there is in certain views a somewhat 

 abrupt swelling of the body, as if from an adhering globule, but none were 

 observed without the enlargement. The ova and spermatozoa in 0. alba would 

 seem to attain full development in February, March, and April ; but the breeding- 

 season of other Ommatopleans ranges from the latter month to November. When 

 fully developed, the mode of depositing the ova and spermatozoa may be illus- 

 trated by the following account : — Two specimens, male and female, of 0. gracilis 

 were taken from a deep vessel, and subjected to examination in a large glass cell. 

 In a very few minutes after the male had been placed on the bottom of the cell 

 tiny jets or jet-like wreaths of sperm-fluid were observed to issue from the sides 

 of the body, rather past the middle, and gradually increased in number, both in 

 front and behind. The body of the animal was soon enveloped in a wavy cloud 

 of the milky substance, whose borders were slowly commingling with the sur- 

 rounding water, while the numerous coiling jets, like so many miniature wreaths 

 of white smoke from the sides of the worm, were constantly adding to the central 

 mass. This operation lasted only a few minutes, and thereafter the animal 

 crawled about the vessel. The female specimen was now observed to protrude 

 her snout from the mass of sand and mucus in which she was coiled, and crawl- 

 ing to the side of the vessel, deposited in a few minutes a group of ova, about 

 three inches distant from the white edges of the sperm-cloud, and she retired 

 again under the mass of sand and mucus. The change of water probably caused 

 the male to eject his matured spermatozoa, and some sympathetic influence, 

 it may be the diffusion of the latter, induced the female at once to evacuate 

 her generative organs, so as to afford the ova the benefit of the male element. 

 A very few ova were found on examination to remain in the body of the female, 

 and they differed in no respect from those deposited in the vessel. The aper- 

 tures by which the respective elements passed out in these specimens were 

 readily observed as pale specks, each furnished with a central opening, round 

 which ciliation for the time being was well marked. These openings, as in 

 Borlasia, occur a little above the lateral nerve-trunk on each side, and even in 

 specimens of O. alba not fully ripened, pressure forces the contents of the 

 generative sacs in the same direction, although no aperture is visible. 



Specimens of O. alba, which had been in confinement for seven months, 

 deposited their ova about the middle of February ; and that this is not later than 

 in the free examples, the receipt of many mature specimens from St Andrews at 



