370 COMPARATIVE ANATOMY CHAP. 



pointed out as formations equivalent to the nephridia of the Annulata (segmental 

 organs). They are said to be in open communication with the body cavity. 



IX. The Connective Tissue. 



The connective tissue found throughout the Crustacean body can here receive 

 only brief attention. Plates, membranes, etc. of connective tissue lie close under 

 the hypodermis and envelop the enteric canal and the sexual organs, and, as 

 neurilemma, the nervous system. Connective tissue strands, fibres, mesenteries, in 

 various places bind the inner organs together and attach them to the integument 

 The lacnnar blood - vascular system, the body cavity, is lined to a great extent, 

 though certainly not continuously, with connective tissue. 



A special form of connective tissue, widely found in Crustaceans, is the fat body, 

 which varies greatly in details. This often envelops the intestine and the heart. 

 In the connective tissue cells of the fat body are found fat-drops, fat-globules, and 

 also often protein granules. The fat body evidently plays a part sometimes larger, 

 sometimes smaller, in metabolism. It is generally variously developed at different 

 ages and times of the year, and also in the two sexes. In the larval forms it is often 

 strongly developed before the moult, which accompanies a metamorphosis, and forms a 

 reserve of nourishment for the process of transformation. In a few Crustaceans, 

 which take no food at the time of sexual ripeness or of the hatching process, it is 

 strongly developed before this time and much reduced after it. 



Connective tissue cells may often become star-like, branched, and occasionally 

 contractile pigment cells. Pigment also occasionally occurs in hypodermal and 

 intestinal cells. 



X. The Sexual Organs. 



The sexes are separate in the Crustacea, except in a few cases 

 which will be duly mentioned. 



The male and female sexual organs are constructed on one type and 

 have a similar position in the body. They are, as a rule, paired. 

 More than one pair never occurs. We can distinguish corresponding- 

 divisions in male and female organs ; viz. first, the germ-preparing 

 organs (ovaries in the female, testes in the male) ; second, the duets 

 of the genital glands (oviducts, in the female, vasa deferentia in the 

 male) ; third, terminal divisions of these ducts, sharply distinguished 

 anatomically and ontogenetically from the preceding (vulva, vagina, 

 reeeptaeulum seminis in the female, muscular duetus ejaeulatorius 

 in the male) ; and fourth, outer eopulatory organs. 



The ovaries and testes cannot in their earliest stage be distin- 

 guished. They can early be recognised as distinct cell groups in 

 the mesoderm, their rudiments can sometimes be traced back to one or 

 two segmentation cells. 



The oviducts and vasa deferentia arise out of the mesoderm 

 apart perhaps from the rudiments of the germ glands. 



The terminal sections of the ducts arise by invaginations of the 

 outer integument. 



The outer eopulatory apparatus consists either of transformed 

 limbs or appendages of limbs, or of processes, folds, prominences, etc. 

 of the integument. 



