The female reproductive organs and secondary sexual characters of Homarus vulgaris are described, in particular the pleopods, which possess seven groups of long non-plumose setæ.
The developing eggs are attached, either directly or by way of other eggs, exclusively to these setæ.
Attachment is by means of strands of transparent “cement” (the funiculus), which also forms the outer membrane of the egg, surrounding an inner membrane which adheres closely to the egg mass.
Chemical and physical tests reveal that the outer membrane has properties identical with those of the superficial cuticle of the integument. The inner membrane is chitinous.
Experiments on the penetration of a variety of substances into the developing egg indicate that the outer membrane has the limited permeability of cuticle, the inner membrane being freely permeable.
The inner membrane is secreted by the oviducal epithelium, the histological character of which varies in relation to egg-laying. Secretion of chitin indicates that the oviduct may be ectodermal.
The outer membrane is formed by cement glands present in great numbers within the pleopods of the female, and these resemble in all respects the tegumental glands which secrete the cuticle.
Secretion by the cement glands is associated with egg-laying, not with ecdysis. The ducts from the glands pass into the interior of the specialized non-plumose setæ, circumstantial evidence indicating that the secretion is discharged through the sides of these. This would explain the attachment of eggs exclusively to these setæ.
In Decapod Crustacea there is an intimate association between ecdysis and reproduction, the sequence of events being outlined.
Available evidence points to fertilization occurring externally in the Astacura, and the complicated structure of the spermatozoa may be correlated with the need for the penetration of the inner chitinous membrane.
Egg-attachment involves low surface tension in the cement, a property already postulated for the cuticle.
The limited permeability of the outer membrane formed by this means renders osmotic hatching possible.
Attachment of eggs in Homarus and allied Decapoda represents the exploitation of a substance which forms the outer covering of the integument and the properties of which—probably low surface tension, slow solidification in water, final hardness, and limited permeability—combine to make it ideal for both purposes.
The sequence of events involved in egg-laying and attachment indicates the probability of control by hormones.
With the exception of the Peneidæ there appears no reason for assuming that the method of egg-attachment differs in any essential particular throughout the Decapod Crustacea.