246 MR. J. D. MACDONALD ON THE ANATOMY OF EURYBIA GAUDICHAUDI. 



is beset with large hepatic lobuli containing cells distended with rich brown-red, yellow, 

 and green fatty globiiles, imparting to them a beautifully variegated appearance. No 

 gastric plates or teeth are visible, though universally present in the true Thecosomata. 

 Having left the stomach, the intestine soon curves forwards to terminate anteriorly near 

 the genei'ative openings, on the right side of the body. 



The salivary secretion is furnished by two irregularly lobulated organs, lined with rather 

 large secreting cells, and lying one on either side of the oesophagus as it emerges from the 

 buccal mass. 



The heart occupies an antero-dorsal position, and its long axis appears to lie transversely; 

 but I have not been able to detect a respiratory organ, or even the actual distribution of 

 the blood-vessels. 



The main centres of the nervous system are the suboesophageal ganglia, which are well 

 developed, and support the auditory capsules containing vibrating otokonia on their 

 inferior surface. 



The ovarium consists of a fan-like expansion of lobuli, on the borders and extremities 

 of which the ova are clustered within the enveloping sheath. From this expansion a 

 number of tubuli arise, and ultimately unite to form a wide oviduct distingmshed from 

 the spermatic duct and intestine by the large longitudinal and nucleated fibres of its mus- 

 cular coat. A large caecal appendage, distended with a bright-orange and plastic fluid, 

 appears to open by a short duct at the same external orifice. This organ is probably the 

 homologue of the so-caUed spermatheca of the Pulmoniferous Gasteropods ; and its con- 

 tained fluid off'ers a remarkable analogy to that occurring in the ovarian sac of some 

 Cephalopods. 



The lobuli of the testis lie upon and coincide so closely with those of the ovarium, that 

 it is difficiilt to distinguish them ; but the stout vas deferens, arising from the point at 

 which the divisions converge, soon communicates, above and a little to the right of the 

 ovary, with a spheroidal sac or vesicula seminalis, which may be readily seen from 

 without, thi'ough the cartilaginous mantle. The spermatic duct thence proceeds forwards 

 in company with the oviduct, and enters the neck of the external male organ, to termi- 

 nate in a perforated dart or rigid point, which occupies the fundus of the inner protrusible 

 membrane of a double-walled pyriform sac having an external orifice near that of the 

 oviduct, on the right side, behind the corresponding swimming-fin. 



The spermatozoa of this Pteropod are remarkable for then* great length and peculiar 

 looping and spirally twisting movements, as illustrated in PI. XLIII. fig. 8 B 6. The fila- 

 ments appear to rotate on their long axes, and twu-l up, like an over-spun thread unlay 

 themselves, and twist up again, with wonderful rapidity while their activity lasts. 



Eim/bia is ovo- viviparous ; and the development of the young may be studied with 

 much interest while yet within the body of the parent. The simple capsule of the ovum 

 ofiers but little for remark ; but the included embryo in the comparatively advanced stage 

 exhibits many points of analogy to that of an ordinary Gasteropod. 



The incipient cartilaginous mantle is of large size compared with the embryo itself. It 

 is globose in figui'e, with an opening at one end, through which the ciliated vela of the 

 young Eurybia may be seen protruding. These latter organs form expanded lobes, lying 



