454 Prof. M'liitosli on the 



the proboscis. By rigid contraction, as formerly racntionerl, 

 the blood can be almost entirely driven from the tentacles. 

 The organs thus capture prey and aid in aerating the blood. 



VIII. The Reproductive System. 



The sexual elements are developed in great profusion 

 from the epithelium of the body-wall of the posterior region. 

 In males the whole space between the dorsal and ventral 

 longitudinal muscles is occupied by a mass of sperm-cells 

 and spermatozoa, especially in summer — the animals, indeed, 

 assuming an opaque greyish hue from this cause. The head 

 of the spermatozoon is shaped like a conical bullet with a 

 j)ointed tip, and two rounded bodies at the base, from the 

 centre of which the elongated tail projects. The movements 

 of the sperms are most active. Many circular cells are also 

 observecl amongst them. 



The ova are similarly developed in the females, in the 

 posterior region, within a very fine limiting membrane or 

 ovary, and quite fill up the perivisceral chamber with the 

 exception of the alimentary canal and the region for the 

 dorsal and ventral blood-vessels. They abounded in examples 

 at the end of June and had attained considerable size. 



In both males and females with developed sexual products 

 peculiar structures occur on each side of the body (invariably 

 on the segment immediately behind the mouth — and in this 

 it first attains perfection), as well as on many of the poste- 

 rior segments, even in those of reproduced tails. In trans- 

 verse section at the tenth segment the central structure is 

 observed to lie within special projections of the body-wall 

 outside the vertical muscle, which is coated by a granular 

 layer. It resembles a folded mass, the folds at first sight 

 simulating a convoluted duct. In the Jiving animal the 

 organ is first noticed in the middle of each segment as a 

 somewhat ovoid projection of the lateral wall, and invested 

 by cuticle, hypoderm, and basement-tissue. It gradually 

 increases in size, and, when fully developed, presents from 

 the ventral surface the form of a semicircular pad on each 

 side. Closer inspection, however, shows that the latter is a 

 tongue-shaped lamella, which curves upward to cover the 

 folded membrane, while superiorly there is a slipper-shaped 

 fold of similar structure which arches over the upper part 

 of the membrane, its edge being incurved laterally aud 

 inferiorly. Such hypodermic folds seem to be formed by 

 an outgrowth and splitting of the body-wall. The peculiar 

 Baembranous structure is thus to some extent exposed to the 



