This section is from the book "General Outline Of The Organization Of The Animal Kingdom, And Manual Of Comparative Anatomy", by Thomas Rymer Jones. Also available from Amazon: A General Outline of the Animal Kingdom and Manual of Comparative Anatomy.
(1104). The reproductive organs are entirely similar to those of Achtheres, already described. Those of the female, represented in the figure, consist of sacciform ovaria, wherein the ova are secreted; and from these, when mature, the eggs are expelled through two simple triangular orifices situated on each side of the anus.
(1105). One of the most singular and anomalous forms of the Epizoa is found in the Nicothoe Astaci, a creature met with in great abundance at certain seasons, attached to the gills of the Lobster, from which it derives its supply of nourishment. This remarkable animal (fig. 223), which is free, and gifted with energetic powers of locomotion during the first periods of its existence, and constructed, at its first appearance from the egg, in perfect accordance with the normal type belonging to its class, ultimately selects for its domicile the branchial chamber of a Lobster, where, fixing itself permanently to the branchial lamellae, it undergoes a complete metamorphosis: its external form is entirely changed; its senses, and means of relation with the external world, become atrophied; singularly-formed excrescences sprout from its sides; and thus transformed, it is content to live beneath the shell of the Lobster, without further intercourse with the external world than is necessary to supply it with the blood which it sucks for food.
Fig. 222. Lamproglena pulchella.
Fig. 223. Nicothoe Astaci.
(1106). The mouth of the Nicothoe is a sort of membranous proboscis, armed near its extremity with styliform points, with which it is enabled to pierce the branchial membrane. Instead of the ordinary more or less flexuous tube which constitutes the alimentary canal in other forms of Entomostraca, the digestive apparatus of Nicothoe consists of two wide sacculi, united together in the median line, in the shape of a horseshoe, from the centre of which a narrow canal proceeds towards the mouth, constituting the oesophagus (fig. 223, b), whilst, derived from the opposite side, another tube of similar calibre runs backwards to the termination of the tail, forming the intestine (c.) The stomach, therefore, is constituted by the two great lateral caeca (g, h), in the interior of which alimentary substances undergo their principal modifications; so that these caeca are evidently analogous to what will be observed in the Pycnogonidae (§ 1112), with this difference, that in those animals the caeca have penetrated into the interior of the ambulatory claws. The thickness of the walls of these stomachal caeca is uniform throughout; they are exceedingly delicate, only exhibiting in their texture some small reddish cells, and are apparently connected to the parietes of the body, in which they are loosely suspended by delicate muscular fraena. (1107.) One very remarkable circumstance presented by the alimentary apparatus of Nicothoe is the peristaltic action of its parietes, which is continued even after its removal from the body, and which here is evidently in relation with the "phlebenterism" exhibited in the arrangement of the digestive system.
No proper respiratory organs exist in these simply-organized beings; the diffusion of the blood through the interior of the body, subservient alike to respiration and nutrition, seems to be entirely effected by the contractions of the intestinal walls; and the proper chylific viscera themselves perform the duties of the lacteal, circulatory, and respiratory apparatus of the higher animals.
(1108). As is the case with the generality of the Lerneans, the male of the Nicothoe was, until recently, unknown to naturalists - a circumstance attributable to two causes: in the first place, the individuals of the male sex are very diminutive in all the genera belonging to this group, insomuch that from their size they seem rather like parasites on the female; and secondly, because in some of them, which have been more particularly studied, a phenomenon is observable analogous with what occurs in the Aphides among insects - there occur whole generations of fertile females, and most probably, also, gemmiparous (nursing) races, during a certain portion of the year, as is the case with Limnadia* and Daphnia1 (§ 1072).
(1109). The male of Nicothoe is represented in fig. 223, 2, magnified in the same proportion as the female. The generative apparatus of the female is largely developed: it is situated principally in the lateral appendages of the body, of which it occupies a considerable part, being lodged by the side of the digestive caeca. The ovarium (fig. 223,1, h) is very irregular in its shape; anteriorly it is bifurcate, and its whole surface has a sacculated appearance. The oviducts (i) become conjoined near the mesial line, and then bend downwards to terminate at the vulva. These canals are frequently filled with ova throughout their whole length. From the oviducts the eggs pass directly into the enormous ovisacs (f), suspended from each side of the caudal portion of the body, between the lateral appendages, in which they are contained until sufficiently mature for exclusion, when the ovisac, bursting, gives issue to hundreds of minute Mcothoes hatched in its interior.
(1110). On emerging from its prison this little creature is exceedingly active, and presents exactly the form of a Cyclops (fig. 223,3); neither would any one ever suspect it to be the same creature which vegetates upon the branchiae of the Lobster. However, no sooner has it fixed itself in that situation than its body begins to swell out laterally, in the shape of two tubercles that sprout from the sides of the body just behind the third thoracic segment, into which the viscera are seen to penetrate; and as these tubercles enlarge, the animal becomes gradually provided with those enormous aliform appendages that are so characteristic of the female adult Nicothoe.